Multiple Atmospheric Rivers Impact California in Early 2017

The state of California has been suffering from a multi-year drought that has severely depleted water resources and reservoir levels. Recent winters have failed to produce precipitation and mountain snows to replenish the losses during the dry summers. However, the situation has rapidly changed this winter, particularly in the past week when multiple atmospheric rivers have impacted the state.

An atmospheric river is a concentrated channel of deep moisture that is transported from the tropical Pacific Oceanic regions to the West Coast of the United States.  These events are often associated with prodigious amounts of rainfall and mountain snows that lead to flooding, mudslides, and avalanches.  We have seen such events this past week impact California, especially the central and northern parts of the state.  CIRA’s total precipitable water product in Figures 1a and 1b depict two separate atmospheric rivers impinging on central California from 8 and 10 January 2017, respectively. The first wave transported a plume of tropical moisture from the south-southwest, which led to massive rainfall and high snow levels.  The second atmospheric river on the 10th was less directly connected to the tropics (coming in from the west-southwest), but nonetheless exhibited a well-focused transport of high moisture content.  Widespread flooding and mountain avalanches have resulted from these moisture plumes as the impacted California, as well as dramatic replenishment of reservoirs.

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Figure 1.  CIRA total precipitable water product (inches) valid at (a) 2100 UTC 8 Jan 2017, and (b) 2100 UTC 10 Jan 2017.

 

SPoRT’s real-time instantiation of the Land Information System (aka “SPoRT-LIS”) has nicely depicted the substantial replenishment of the moisture content in the soils over California.  The SPoRT-LIS is an observations-driven, ~3-km resolution run of the Noah land surface model that consists of a 33-year climatology spanning 1981-2013, and real-time output at hourly intervals sent to select NOAA/NWS partnering forecast offices.  The one-year change in the SPoRT-LIS total column soil moisture at 1200 UTC 11 January (Fig. 2) shows large increases over most of California, particularly in the higher terrain (given by blue and purple shading).  [At the same time, annual degradation in soil moisture can be seen across the central and eastern U.S.]  Interestingly, a substantial portion of California’s annual soil moisture increases has occurred in just the past week (Fig. 3; SPoRT-LIS total column soil moisture change over the past week).  One can certainly see the important role that atmospheric rivers play in being “drought busters”!

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Figure 2.  One-year change in the SPoRT-LIS total column relative soil moisture, valid 1200 UTC 11 January 2017.

 

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Figure 3.  One-week change in the SPoRT-LIS total column relative soil moisture, valid 1200 UTC 11 January 2017.

 

A map of the SPoRT-LIS daily soil moisture percentiles from 11 January highlight the very wet anomaly over California relative to the 33-year soil moisture climatology (Fig. 4; similar to the pattern of annual soil moisture change from Fig. 2).  Blue shading denotes greater than or equal to the 98th percentile, thus indicating unusually wet soils on the tail end of the historical distribution.

fig4_rsm02percent_20170111_12z_conus

Figure 4.  SPoRT-LIS total column relative soil moisture percentile from 11 January 2017.

 

Finally, SPoRT is acquiring and assimilating in real time the Soil Moisture Active Passive (SMAP) Level 2 (L2) retrievals produced by NASA/JPL into an experimental version of the SPoRT-LIS.  SPoRT is a SMAP Early Adopter and has a funded project to conduct soil moisture data assimilation experiments with LIS and evaluate impacts on land surface and numerical weather prediction models.  Figure 5 shows SMAP L2 retrievals of the evening overpasses from ~0000 UTC 11 January.  Panel (a) is the 36-km resolution radiometer product, while panel (b) shows the enhanced-resolution product, obtained from the SMAP radiometer by using Backus-Gilbert optimal interpolation techniques to provide data on a finer (9 km) grid.  The enhanced-resolution product provides much more detail of the wet soils in California, while retaining the same overall regional patterns as the original 36-km retrieval.  Given the loss of the active radar component of the SMAP mission, SPoRT plans to assimilate both the 36-km and 9-km products separately, and compare results on model accuracy.

fig5_smap-l2-11jan2017

Figure 5. SMAP Level 2 soil moisture retrievals for the evening overpasses from ~0000 UTC 11 January 2017; (a) 36-km resolution product; (b) enhanced 9-km resolution product.

Stark contrast in Eastern U.S. soil moisture following Hurricane Matthew

Stark contrast in Eastern U.S. soil moisture following Hurricane Matthew

Major Hurricane Matthew left a trail of destruction in its wake from the Caribbean up through the U.S. East Coast.  As Hurricane Matthew tracked northward along a large portion of the U.S. Southeast Coast from Florida to North Carolina, the rainfall impacts worsened.  Figure 1 shows the weekly rainfall spanning 4-11 October, ranging from ~2-8 inches along the Florida East Coast to 10-20 inches in the eastern Carolinas.  Since antecedent soil moisture was highest in the eastern Carolinas (Fig. 2), the extreme rainfall led to the most serious flooding in this area.

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Fig. 1.  Weekly rainfall totals from 4 – 11 October 2016.

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Fig. 2.  Total Column (0-2 m) relative soil moisture prior to Hurricane Matthew’s impact on North and South Carolina, valid at 0000 UTC 7 October 2016.

Referring back to the precipitation totals in Fig. 1, we can see that there was a sharp rainfall gradient on the northwestern edge in the Middle Atlantic region.  Interestingly, this gradient in Hurricane Matthew’s rainfall coincided with a pre-existing transition zone between wet conditions near the Atlantic coast and drought conditions further inland from the Appalachians through New England.  The net result was to accentuate the wet-dry contrast already in place.  The animation in Fig. 3 highlights this contrast nicely by presenting the SPoRT-LIS daily total-column relative soil moisture percentiles from 1-12 October.  The percentiles are based off a 1981-2013 daily soil moisture climatology that SPoRT produced from its ~3-km resolution SPoRT-LIS simulation.  By 9 October, notice the incredible transition from excessively wet soil moisture exceeding the 98th percentile (Carolinas through the southern half of Delaware) to extremely dry soil moisture less than the 5th percentile across Pennsylvania into the Northeast (as well as much of the inland Southeastern U.S.).  In fact, total column soil moisture values are less than the 2nd percentile over a large part of Ohio, Pennsylvania, New York, and the New England states, indicative of the ongoing severe drought there.

fig3_loop

Fig. 3. Daily animation of SPoRT-LIS total column relative soil moisture percentile from 1 to 12 October 2016.

Transition to CONUS SPoRT LIS Underway…

So, we’ve finally begun the process of transitioning over fully to the new CONUS version of the SPoRT LIS.  This “new” version of the SPoRT LIS has been under development actually for several years now, and underwent initial testing and evaluation at the Huntsville WFO in spring 2015, followed by an evaluation by several WFOs and RFCs in summer 2015.  Image 1 below shows the differences in the domains.  The new version of the SPoRT LIS encompasses the entire CONUS and surrounding areas of southern Canada and northern Mexico, albeit with some anticipated degradation especially in the border regions due to lack of consistent radar/precipitation coverage.

lispostimage1_28sep2016

Image 1. The CONUS SPoRT LIS (left) and the approximate domain of the old Southeast CONUS version (right).  Note: the images are from different periods.

Not only does the CONUS version offer a geographic expansion over the previous version of the LIS, but new variables are a part of the new SPoRT LIS, including 0-200 cm relative soil moisture changes on several timescales (weekly, bi-weekly, monthly, seasonal, semi-annual and annual) soil moisture percentiles and soil temperatures.  The soil moisture percentiles and change values can be especially useful for the drought designation and analysis process, and have been used in this capacity at the Huntsville office since their inception.  Of course, there are other applications for hydrology, fire weather and blowing dust.  We’re planning to explore more of these latter unique and interesting applications with several of SPoRT’s collaborative Western CONUS WFOs next spring and summer.  The SPoRT LIS soil temperature data have shown promising application for impacts during winter weather events during evaluation of a few events in the previous winter, with more evaluation expected during the upcoming winter.  In addition to the new variables, the new version of the SPoRT LIS is using NSSL’s Multi-Radar Multi-Sensor data for precipitation forcing in the near term and is also solely incorporating the VIIRS GVF over the legacy MODIS GVF.

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Image 2. Examples of SPoRT LIS 0-200 cm relative soil moisture weekly change (left) and 0-200 cm relative soil moisture percentile (right)

Users of the SPoRT LIS and GVF data for their local modeling purposes will need to make the appropriate changes to their EMS/UEMS model runs to properly incorporate these new data sets.  Please contact Jon Case at SPoRT or me (Kris White) if you have any questions.  Thanks for reading!

Louisiana Flooding Captured by SPoRT-LIS

About a week ago, southern Louisiana began to experience heavy rainfall from a storm system that remained relatively stationary over the Gulf Coast.  The SPoRT-LIS, a real-time, high-resolution implementation of the the NASA Land Information System, captured trends in soil moisture that provide some insight into the evolution of this flooding, including hints at precursor conditions that may have led to the extreme nature of this event.

The 0-200 cm integrated relative soil moisture (RSM) fields have been used in the past to identify flood precursor conditions.  These fields give an indication of the total amount of water in the soil moisture column and provide information about how much additional precipitation can be accepted by the soil before all becomes runoff into nearby streams and rivers.  About 2 weeks ago (August 3 00Z; Fig. 1), Southern Louisiana showed soil moisture values in the 50% range, which are higher than other parts of the country, but likely about normal given the swampy nature of that region.  However, following a couple of precipitation events in that area on August 3, 7, 9, and 10), these integrated RSM fields bump up the 60-65% range (Fig. 2), which has become somewhat of an unofficial threshold for antecedent saturated soils that could lead to areal flooding events.  Based on various reports, it appears that the official start of the flooding event began on August 11.

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Fig. 1: SPoRT-LIS valid at 00Z on 03 August 2016 showing 0-200 cm integrated relative soil moisture values around 50% over Southeastern Louisiana.

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Fig. 2: SPoRT-LIS 0-200 cm integrated relative soil moisture values valid at 00Z on 10 August 2016 showing impact of multiple precipitation events since the 03 August figure above. Soil moisture values are elevated in southeastern Louisiana to values around 60-65%.

 

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Fig. 3: SPoRT-LIS 0-200 cm integrated relative soil moisture values valid at 00Z on 14 August 2016 following the heaviest precipitation. Soil moisture values are above 90% in most areas, indicating major ongoing flooding across much of southern Louisiana.

Starting on 11 August, the 0-200cm integrated RSM begins to exhibit signs of flooding (starting to get into 70-80%; not shown).  By Aug. 12, most of SE LA is above 80% Integrated RSM with pockets above 90% (not shown).  By Aug. 14 (Fig. 3), nearly all of southern Louisiana is covered with soil moisture values above 85-90%, which indicates major ongoing flooding in this area.

These products are provided to select National Weather Service partner offices to aid in these flooding forecast challenges.  For more details on this product and to view additional days or hours, please visit the real-time SPoRT-LIS page.

U.S. Deep South flooding as depicted by NASA’s SMAP satellite and SPoRT-LIS

U.S. Deep South flooding as depicted by NASA’s SMAP satellite and SPoRT-LIS

A significant flooding event occurred over the U.S. Deep South from 8-10 March 2016 due to a slow-moving low pressure/front from southern Texas to the Mississippi River, combined with a deep tropical moisture plume.  Tremendous rainfall totals of 4-8″+ were depicted by the Multi-Radar Multi-Sensor (MRMS) 1-km gauge-corrected radar rainfall estimate product for consecutive 24-hour periods ending 1200 UTC 9 March and 10 March 2016 (Fig. 1).  The MRMS gridded product provides short-term input precipitation estimates to the real-time Land Information System (LIS) run at the NASA Short-term Prediction Research and Transition (SPoRT) Center.

Fig1_MRMS2dayPrecip

Fig. 1.  Rainfall estimates from the Multi-Radar Multi-Sensor (MRMS) gauge-adjusted radar product for the 24-h period ending (a) 1200 UTC 9 Mar 2016, and (b) 1200 UTC 10 Mar 2016.

The soil moisture response to the heavy rainfall was captured nicely by NASA’s Soil Moisture Active-Passive (SMAP) satellite Level 2 retrieval product of 0-5 cm volumetric soil moisture for the early morning overpass across the Central U.S from 9 March (Fig. 2a).  Very high retrieved volumetric soil moisture of 0.45 or higher is seen from eastern Texas across much of northern Louisiana and southern/central Arkansas, aligned well with the areas that received the heaviest rainfall.  The corresponding SPoRT-LIS modeled soil moisture analysis for the 0-10 cm layer of the Noah land surface model (Fig. 2b) shows a reasonable agreement with the SMAP retrieved soil moisture but with slightly less dynamic range than the SMAP data — a reasonable result given that the SMAP retrieval is valid over a shallower, near-surface layer than the LIS top model layer.

Fig2_SMAPL2_LIS

Fig. 2.  (a) Soil Moisture Active-Passive (SMAP) 0-5 cm volumetric soil moisture retrieval valid 1223 UTC 9 Mar 2016, and (b) corresponding SPoRT-Land Information System (LIS) 0-10 cm volumetric soil moisture analysis valid 1200 UTC 9 Mar 2016.

The SPoRT-LIS total column relative soil moisture (RSM) has been found to qualitatively correlate with areas of river/areal flooding when exceeding ~60% across northern Alabama.  The depiction of total column RSM from the early morning of 10 March shows a large area exceeding 65% (blue  shading in Fig. 3a) across eastern Texas, northern Louisiana, and southern/central Arkansas.  The weekly change in total column RSM (Fig. 3b) highlights the regions that experienced the largest increases in soil moisture in response to the heavy rainfall.  As the soil approaches saturation/field capacity, most new rainfall goes directly to runoff, thereby exacerbating the flooding situation.

Fig3_LISrsm02m

Fig. 3.  SPoRT-LIS analysis valid 1200 UTC 10 Mar 2016 of (a) total column relative soil moisture (RSM), and (b) one-week change in total column RSM.

Another product available from the real-time SPoRT-LIS is the total column RSM percentile, which shows how anomalous the current soil moisture conditions are relative to a historical, 33-year climatological database of modeled soil moisture. The percentile product from the morning of 10 March (Fig. 4) shows that areas of eastern Texas and northwestern Louisiana (and a few other spots) exceed the 98th percentile for the current day — indicating that these present-day soil moisture values are about the most moist it has been in the last 33+ years for 10 March.

Notice that there are a few anomalous “bulls-eyes” of dry percentiles in southern/eastern Arkansas.  These areas are caused by corrupt input precipitation data driving the SPoRT-LIS land surface model simulation.  The issue is currently being corrected by the operational organizations managing the rain gauge input.  However, it should be noted that SPoRT is working to implement near real-time data assimilation of the SMAP Level 2 soil moisture retrievals into its LIS simulation.  Routine assimilation of SMAP satellite soil moisture will help correct anomalies caused by poor input precipitation, thereby resulting in more robust soil moisture analyses for situational awareness and disaster-response applications.

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Fig. 4. SPoRT-LIS total column RSM percentile valid 1200 UTC 10 Mar 2016.

Finally, the areas of active flooding at U.S. Geological stream gauges and the NOAA/NWS flood watch/warning map are given in Fig. 5 for the afternoon of 10 March.  The axis of flash flood warnings (dark red color) aligns quite well with the total column RSM percentiles exceeding the 98th percentile in Fig. 4, whereas the broader footprint of all flood warnings/watches corresponds closely with the total column RSM above the 65% value (blue shading in Fig. 3a).

Fig5_flooding

Fig. 5.  Plot of U.S. Geological Survey stream gauges with active flooding (top), and NOAA/NWS active [flash] flood watches and warnings (bottom-right) for the afternoon of 10 Mar 2016.

LIS Soil Temps and the Unfolding Winter Storm…

The current winter storm unfolding across the eastern U.S. may be the storm that launches a thousand blog posts.  Well, maybe at least two or three on this site.  We’ll see.  Anyway, there may be multiple opportunities to assess the utility of a variety of Proving Ground (PG) data sets and imagery during this event.  Although not a PG suite of products, I’m going to start by taking a quick look at the SPoRT LIS soil temperature data that are being delivered to several NWS offices, including my own (Huntsville).

Below is a brief loop of 0.5 degree composite reflectivity imagery from the NWS NEXRAD network.  The great thing about AWIPS II, is that with some manipulation of time options, the radar loop can be layered over the latest LIS soil temperature data.  In this case, the latest data available were from 09Z this morning.

Radar_LIS09Z_loop

NASA SPoRT LIS 0-10 cm soil temperatures (image, F) valid at 09Z 22 Jan 2016, overlaid with WSR-88D 0.5 degree composite reflectivity, 1324Z-1512Z.  Surface observations in yellow. 

The soil temperature data have been color coded so that white colors represent the transition zone where temperatures are around freezing (28F to 34F), per the model, and impacts may be occurring or beginning to occur.  Of course, there are other factors to consider, such as precipitation type at the surface, and precipitation intensity.  If precipitation is liquid, then soil temperatures in the upper 20s will likely translate into  an icing event.  However, if temperatures are at or just below freezing, latent heat release generally will warm the very shallow layer near the surface, leading to eventual melting of any ice that accumulates.  If soil temperatures are above freezing, say around 34F, snow can still accumulate on the surface, as long as the snowfall rate exceeds the snow melt rate.

Looking at the data and imagery above, it would appear that much of Tennessee is under threat of some type of freezing precipitation at the surface, whether from accumulating snow or freezing rain.  Taking a closer look, the observation at Knoxville starts out at 36F in this loop, and finishes at 35F by the end of the loop with rainfall being reported.  Soil temperatures there are right around 32F to 33F at closer inspection.  So, no real good chance of freezing precipitation at the surface.  But, the data show forecasters that ground temperatures will not have to fall much before there are potential issues, especially as colder air begins to move into that area.  However, per reports from Nasvhille and many surrounding locations in middle and western Tennessee, snowfall is accumulating rapidly where soil temperatures (per closer inspection in AWIPS) are around 31F to 32F.  Meanwhile, reports of accumulating snowfall have been received from portions of northern Mississippi and southwestern Tennessee, where 0-10 cm soil temperatures are generally in the 34F to 38F range.  So, these are locations where the snowfall rate certainly exceeded the melt rate of the snow at the surface.  Nevertheless, the ground will continue to radiate these higher temperatures into the shallow snowpack and some melting from beneath will likely occur through the day.  These are other ways the data can be used…to determine the potential length of lingering impacts from recent snowfall.  Some limitations to the data currently?…they are only at 3 hourly resolution and have about a 2-8 hour latency.  We might want to reconsider higher temporal resolution during times of inclement winter weather, where more rapid updates would be more operationally useful.  Anyway, this is something for the SPoRT modeling team to explore.

These data are becoming a very valuable tool during operations at our office and several others.  Just yesterday, the Raleigh NC NWS office cited the data when assessing the potential for accumulating snow and ice in their forecast area.

 

Recent rains and changes in soil moisture in the Southern Plains…

Significant rains have fallen across portions of the Southern Plains recently.  Widespread rainfall amounts from eastern New Mexico across northern Texas and southern Oklahoma total around 2-4 inches.  Isolated locations have received around 6-8 inches, and most of this has just fallen in the past few days (image 1).

7-Day Observed Precipitation over the Continental U.S., courtesy of the National Weather Service.  Data ending 12 UTC 23 Oct 2015.  Notice the heavy rainfall across the Southern Plains.

Image 1.  7-Day Observed Precipitation over the Continental U.S., courtesy of the National Weather Service. Data ending 12 UTC 23 Oct 2015. Notice the heavy rainfall across the Southern Plains.

More rain is on the way, especially for eastern portions of Texas and the southern Mississippi Valley over the next couple of days as a plume of deep tropical moisture and the remnants of Hurricane Patricia become swept into the region ahead of an advancing trough of low pressure.  Numerous flash flood watches and warnings have been posted for much of this area.  Interestingly, parts of this same region, are still considered in D4 drought, due primarily to very dry conditions that have persisted since the summer months (image 2).

Image 2.  US Drought Monitor over the South Region, 20 October 2015

Image 2. US Drought Monitor over the South Region, 20 October 2015

Drought reductions will very likely be in order with upcoming weekly issuances of the Drought Monitor.

Soil moisture across the region, per the 3-km SPoRT LIS has increased dramatically, especially the shallow layer soil moisture.  I thought I’d take a moment to share a loop of 0-10 cm Relative Soil Moisture values during the past few days.  These values go from as low as ~5% in the beginning of the image across a large swath of Texas to ~70-80%, especially in northern parts of Texas and around the DFW metro area.  Further rains in the area of recently, nearly saturated soils will only increase the risk for runoff and the potential for further flooding.  These data are being ported into some NWS offices to aid forecasters in situational awareness for the risk for flooding and for drought analysis.  Little did some forecasters know that they would have the opportunity to utilize the data for both purposes in the same week!  Having the data in AWIPS is just one advantage of the SPoRT LIS data.  Other advantages are the spatial resolution (3 km) and the temporal latency (~2-8 hours).  This relatively short latency over other legacy soil moisture data sets is possible due to the incorporation of MRMS precipitation data for forcing the model in the shorter term (~<4 days).

Image 3.  SPoRT LIS 0-10 cm Relative Soil Moisture, 21 UTC 21 Oct to 15 UTC 23 Oct 2015.

Image 3. SPoRT LIS 0-10 cm Relative Soil Moisture, 21 UTC 21 Oct to 15 UTC 23 Oct 2015.  (you may need to click on the image to see the loop)

Of course, soil moisture will be slower to increase in deeper layers, as this recent depiction of 0-200 cm Relative Soil Moisture shows.  Nevertheless, look for future increases in this deeper layer over the next couple of days.

Image 4.  0-200 cm Relative Soil Moisture 15 UTC 23 Oct 2015.

Image 4. 0-200 cm Relative Soil Moisture 15 UTC 23 Oct 2015.