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Area Forecast Discussion
Issued by NWS Paducah, KY
Issued by NWS Paducah, KY
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291 FXUS63 KPAH 131104 AAA AFDPAH Area Forecast Discussion...UPDATED National Weather Service Paducah KY 604 AM CDT Tue Aug 13 2024 .KEY MESSAGES... - Humidity increases west to east through the day. - An axis of heavy rain may set up over southeast Missouri tonight, leading to flash flood potential - but the exact placement remains uncertain. - Scattered thunderstorms will probably become more numerous by Thursday night as a front approaches. There is some severe and flash flood risk with this activity although things are not set up exactly right for it. && .DISCUSSION... Issued at 207 AM CDT Tue Aug 13 2024 Flow aloft this morning is out of the northwest with a distinct shortwave over SWIN. This seems to be responsible for some very light showers over this region but they only have an extremely thin layer of moisture just below the residual subsidence inversion to work with and most rain is probably not quite reaching the ground. That activity should be well clear by sunrise with residual high clouds rounding the trough. As often occurs with this pattern dewpoints range from 60-62 over Indiana to the lower 70s over central Arkansas. As the primary ridge axis aloft moves eastward through the day this area of richer low and deep column moisture moves with it, moving over southeast Missouri by late afternoon. This increase in moisture may spark showers and elevated thunderstorms by late afternoon but it will have to fight against some initially marginal thermodynamics. As the ridge axis moves further east by sunset the region falls more under the right exit region of the polar jet maximum oriented to our north. Most guidance then develop two distinct shortwave troughs moving through late Tuesday afternoon and then early Wednesday morning. This should help improve our thermodynamic situation to the point convection becomes more likely in the areas of deeper moisture over southeast Missouri. Northwest flow over a moisture gradient with PWATs >2.00+ is a common heavy rain/flash flooding pattern for us. HREF 24 hr PMMs show 4 to 7 inches over Carter and Ripley Counties. Discussed a flood watch with neighbors and WPC but the marginal thermodynamics and uncertainty on exactly where an axis of heavy rain would set up precludes us this morning. Will however increase the tone of flood messaging with this forecast package. The large scale ridge axis moves roughly overhead Wednesday. Some guidance show a weak shortwave moving through this flow but with the subsidence of the large scale ridge - think the thermodynamics may be more unfavorable for convection. Although the depth/richness of the column moisture precludes us from keeping the forecast dry. All of this is being nudged eastward by a zonal polar jet max capped off by a fairly strong shortwave trough. Guidance is coming into better agreement on the timing and details with this trough moving through Thursday night. Instability is marginal on weak mid level lapse rates, but its conceivable that a window opens up late Thursday afternoon and evening for at least some severe risk given the favorable deep layer shear profile and marginal low-level shear profile coupled with available moisture. High column moisture will make flash flooding a potential concern as well. The surface front however is slow to move through weak convergence in the warm sector during peak heating. GFS/NAM also show DCVA behind a leading shortwave trough which may lead to poorer thermodynamic instability further limiting severe/convective potential. 00z ECMWF is a little slower with the frontal passage where the GFS brings it through cleanly by Saturday owing to more sharpness in the overall trough. I tend to prefer the faster solution given ensemble members from both camps. A new trend in the 00z suite is to be stronger with the advancing upper ridging over the four corners region which puts us back in a boundary northwest to southeast with thunderstorms under northwest flow by Sunday but ridging builds much stronger through Monday and breaks this pattern up. NBM doesn`t bite off on any PoPs with this pattern and its close enough to not argue too much at this point, will see if that trend continues through the next 12-24 hours. && .AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/... Issued at 604 AM CDT Tue Aug 13 2024 VFR conditions are expected today under passing high clouds and light winds. Tonight convection may become a factor over southeast Missouri or slightly further east. Fog may settle in to parts of southeast Missouri as well as increased low level moisture works its way eastward through the overnight hours. More widespread convection is possible further east by around daybreak. && .PAH WATCHES/WARNINGS/ADVISORIES... IL...None. MO...None. IN...None. KY...None. && $$ DISCUSSION...JGG AVIATION...JGG