Evaluations of the NESDIS Quantitative Precipitation Estimate (QPE) and CIRA Layered Precipitable Water (LPW) products have been ongoing for a portion of March at three of SPoRT’s collaborative West Coast NWS offices (Monterey, Eureka, and Medford). The GOES-R QPE is an experimental satellite-based precipitation estimation algorithm using both IR and microwave data from the GOES-East and West satellites. A suite of products are currently being generated and ported into AWIPS I, including a 15-minute rainrate product and several accumulation products on timescales of 1-hour, 3-hours, 6-hours, 1-day, 3-days and 7-days. The IR and microwave data used to generate the QPE have different timescale resolutions, about 15 minutes and 1+ hours, respectively. IR data are used to infer cloud top temperatures and heights, and rainfall rates are derived from this information. Further calibration with microwave data from the TRMM and NOAA 18/19 helps to fine-time the precipitation accumulations. However, calibration with tropical environments does not always necessarily translate well in mid-latitude environments, even coastal marine environments. As a result, precipitation in areas with relatively think cirrus clouds can be overestimated, while the QPE product is thought to perform better in convective situations for operational purposes.
Unfortunately, during the evaluation period, precipitation has generally been below normal, but a couple of events have allowed for a few evaluations of these products so far.
First, the good…
On March 16th, one forecaster noted that the QPE and LPW data were useful for helping to “comfirm that heavy precipitation was not going to be a factor with the incoming front. QPE was small offshore, and TPW matched model TPW pretty well.” Below are images of the QPE (Image 1) and LPW (Image 2) as viewed through AWIPS at that time.
Figure 1. NESDIS QPE 6-hour accumulation (inches) product valid 0600-1200 UTC 16 March
Image 2. CIRA Layered TPW product valid 1500 UTC 16 March. From upper left, clockwise: Total precipitable water, surface-850mb LPW, 700-500mb LPW, 850-700mb LPW
Although relating that the impacts of the LPW product to the forecast process were small, the forecaster did express high confidence in the values and asserted that the value of the layered PW product over a standard total column product was large. With increased forecaster confidence, details about the incoming storm moisture were noted in the Area Forecast Discussion that morning.
I am eager to evaluate this product over the upcoming weeks, especially during strong moisture advection events concurrent with low or mid-level jets. It will be interesting to see if having satellite-based information about the vertical distribution of moisture and determining intersecting regions of isentropic lift within these vertical layers will provide better assessments of precipitation.
Now, for the not so good…
The QPE product has tended to overestimate precipitation where cold, thick cirrus clouds are present, making it difficult or impossible to infer reasonable precipitation amounts from the QPE product alone. On March 20th, a survey respondent noted that “with so much high-level cold cloud tops, the QPE product was virtually unusable.” In this particuar case, of mostly stratiform precipitation ahead of a frontal boundary, the QPE product far overestimated precipitation east of the Cascades in southern Oregon and underestimated the rainfall near and along the coast. Notice the swaths of heavy rainfall across northern CA and SE Oregon in the QPE product in Image 3. However, notice the general lack of precipitation in these areas per the Stage-III product in Image 4 below.
Image 3. NESDIS 24-Hr QPE product for Oregon and sourrounding areas, valid for the period ending 1200 UTC 20 March
Image 4. Stage-III 24-Hour precipitation totals for the period ending 1200 UTC 20 March
The forecaster went on to state that “perhaps [the QPE] will be better in the summer with convection…or perhaps in the next few days with the colder NW flow showery regime.” Indeed, this product is expected to perform better in such situations.
Despite some of the limitations discussed so far, these products do show potential for assessing atmospheric moisture content and precipitation. The SPoRT team and our collaborative offices will be conducting further evaluations of both stratiform and convective precipitation cases on the West Coast and elsewhere to provide input about these potentially valuable products.
Thanks to Anita LeRoy, Geoffrey Stano and Kevin Fuell for help in providing imagery for this post.
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