United States Quantitative Precipitation Forecast (QPF) |
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Quantitative Precipitation Forecast Discussion NWS Weather Prediction Center College Park MD 532 AM EDT Tue Jun 05 2018 Final Day 1, Day 2 and Day 3 QPF Discussion Valid Jun 05/1200 UTC thru Jun 08/1200 UTC Reference AWIPS Graphics under...Precip Accum - 24hr Day 1 ...Northern Plains - Upper Mississippi Valley... Upper ridge axis pushes east of the northern Plains and Upper MS Valley region Tue night. In its wake, an uptick in broad scale upper forcing (divergence aloft) will ensue, and get a considerable boost within the right entrance region of an upper level jet streak traversing southern Ontario. Meanwhile, the increasing (and veering) nocturnal LLJ will lead to rapid low-level moisture/theta e transport ahead of a sharpening frontal zone. Both synoptic and thermodynamic indicators give credence to the the multi-model signal of a developing MCS overnight along the "ring of fire", though as is typical, the model solutions are not well clustered with respect to the details in terms of MCS track and thus axis of heaviest rainfall. WPC did nudge the QPF axis a little father south from the previous forecast -- essentially in line with the blend of the WRF-ARW, ARW2, and NSSL-WRF (all of which aligned reasonably well, while the NAM CONUS Nest, WRF-NMMB, NBM, and global guidance were farther north. Despite the fairly vigorous mid-level cap, based on climo like the aforementioned high-res depiction of the heavy rainfall footprint farther south, along and north of the surface boundary where the coupling of robust deep-layer elevated instability and moisture transport will be maximized north-northeast of the 700 mb +12C isotherm. Also supporting a more southern solution of the MCS track/heaviest QPF would be the degree of southward propagation overnight, as the s=sw LLJ begins to exceed the speed of the mean 850-300 mb flow. At this point, the progged shear profiles would support a progressive MCS; however, multiple rounds of convection as noted from the ARW/ARW2 (first one along the initial wnw-ese warm frontal boundary) could pose a more enhanced flash flood risk across far northeast SD and southeast ND. ...Central Gulf Coast Region... Mid-upper shortwave trough -- bolstered early in the period the MCV over the ARKLATEX -- will be the catalyst for additional diurnally-enhanced convection along the surface stationary front south toward the Gulf coast. 0-6km bulk shear values aoa 25 kts along with robust deep-layer instability (mucapes at 2000-3000+ j/kg) will support more organized, widespread coverage during the afternoon through mid evening ahead of the upper trough, with the surface moisture convergence getting an added boost from the developing Gulf breezes. Despite the relatively high 1-3 hourly FFG (generally 2.5-3.0" in 1 hour and 3-4" in 3 hours), localized totals of 3-5" within a few hours per the high-res CAMs would support a marginal risk of excessive rainfall, particularly over portions of se LA given the relatively wetter antecedent soils (lower FFG values). Hurley Day 2 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER THE CENTRAL PLAINS... ...Northern Rockies to Central Plains... Weak shortwave energy rounding a broad mid-upper level ridge axis extending up the high plains will cross the north-central Great Plains Wednesday. A low level jet under the ridge will bring Gulf moisture north with 1.5 inch PW over NE/IA which is two standard deviations above normal. The combination of high moisture, instability, and mid level forcing should be enough to break the cap and trigger scattered heavy thunderstorms that will shift southeast in the anticyclonic flow. MCS development is likely given the strong instability and expected forward propagation. QPF was based on a blend of the 00Z GFS/NAM/ECMWF and in-house bias-corrected blend. The marginal risk is for the main convective storm breeding ground east of the Sand Hills where 6-hr FFG is generally 2 to 2.5 inches. Progression of organized/MCS activity may need to be accounted for in subsequent QPF and ERO. ...Florida... A swath of 1.75 inch PW along a stalled front will allow heavy rain across central FL. Light easterly mean flow could allow repeating cells off the Gulf. FFG is quite high in central FL, so flash flooding is likely limited locally. Day 3 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER THE CENTRAL PLAINS AND NORTHERN HIGH PLAINS... ...Northern Rockies to Central Plains... Weak shortwave energy rounding a broad mid-upper level ridge axis extending up the high plains will cross the northern Great Plains Thursday. A wake from Wednesday activity should exist over the north-central plains Thursday with development likely initiation along remnant boundaries. 1.25 to 1.5 inch PW is 1.5 to 2 standard deviations above normal. Instability is progged to be stronger over the Central Plains then MT which may allow for greater MCS development. More details on mesoscale processes on subsequent forecasts. QPF was based on a blend of the 00Z GFS/NAM/ECMWF and in-house bias-corrected blend. The marginal risks over MT and NE/KS/IA is based on 00Z consensus for the low position along with more sensitive FFG. Hurley/Jackson Graphics available at www.wpc.ncep.noaa.gov/qpf/qpf2.shtml |
