Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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105 FXUS63 KOAX 221957 AFDOAX Area Forecast Discussion National Weather Service Omaha/Valley NE 257 PM CDT Wed Mar 22 2017 .SHORT TERM...
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(tonight through Saturday) Issued at 256 PM CDT Wed Mar 22 2017 Milder and more active pattern is at our doorstep. Subjective 12Z upper-air analysis indicates broad upper-level ridge across the central US, with 500mb height falls up to 60m over the Rockies to southern CA. Southwesterly upper-level jet streak up to 95kt was noted from southern/central CA to ID. An 850mb ridge was noted through the Mississippi River valley, with southerly winds over the High Plains. Moisture was returning northward through TX into OK, along with warmer 850mb temperatures from the southern Plains to the northern Rockies. Surface lee trough at 18Z was noted in eastern WY/eastern CO, with high pressure over MI and southeasterly surface winds across the mid-Missouri River valley. Surface dewpoints were still in the teens to lower 20s, with higher dewpoints well south in TX/OK, but temperatures were moderating into the mid-40s to lower 50s even with thinning clouds. Main forecast concern through Saturday is potential for precipitation as an upper-level trough moves into the Rockies through Thursday, then closes into a low as it ejects across KS/MO Friday. Agreement in trajectory and timing is good for this first of several lows, leaving some devil in the details of rain onset and placement. Strong warm/moist air advection tonight should bring stratus and perhaps some drizzle and fog through Thursday morning. Think anything more showery would hold off until afternoon, if it falls at all (GFS is something of an outlier here in precipitation extent). Also have held off any mention of isolated thunder until after midnight Thursday night, as forecast soundings struggle to support elevated instability until maybe very late. Have very little temperature fall-off tonight, and have bumped max temperatures down in the northern half of the CWA, which is more likely to remain cloudy longer, but bumped up a touch on the southern border, where clearing and dry slotting may allow some warm air to surge northward. Coverage of showers/rain will increase on Friday as upper-level low ejects, with surface low also sliding across KS/MO. Though the CWA will mainly be on the cold side of the low, the temperature difference is not stark, and precipitation should remain all rain. That said, it may take on a banded character somewhere in northeast NE/northwest IA, with higher rainfall amounts. Kept spotty isolated thunder mentions on Friday, but not terribly confident in thunder potnetial so far north of the low in a cooler and saturated airmass. Rain may linger through Saturday morning, especially in the eastern CWA. Am suspicious that the diurnal swing of temperatures Thursday night through Saturday may be too broad, especially in the northern CWA, with lingering clouds and rain - the lows may be too low and the highs too high. .LONG TERM...(Saturday night through Wednesday) Issued at 256 PM CDT Wed Mar 22 2017 Active pattern continues through next week, with more upper-level lows progged to cross the southern to central Plains and toward the mid-MS River valley. The coherency (model agreement) of each wave decreases with time, of course. The next wave looks likely to eject across KS-MO on Sunday/Monday. Indications are that it will be a closed low that opens into a wave as it moves across the Plains. Have trended downward on precipitation chances on Sunday night through Monday midday as the trough and associated precipitation linger more in KS-MO. After a respite on Tuesday, a deeper low is progged to cross the Plains on Wednesday-Thursday, with the initial effects at the end of this forecast package. With considerable uncertainty regarding the placement and speed of the low, the best we can say now is that there may be some potential chances for rain on Wednesday in advance of the low.
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&& .AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon) Issued at 103 PM CDT Wed Mar 22 2017 Weak short wave exiting the area early this afternoon, and as such mid-level subsidence overspreading the area. Isentropic upglide persisting 305K and below, allowing VFR ceilings 8-12K to persist at all three TAF sites. Expect VFR conditions to continue through the first 8 hours of the TAF cycle, with deteriorating conditions thereafter. Access of H5 ridge will shift eastward, and will allow deep, moist ascent to invade northern plains. Developing LLJ will result the advection of MVFR then IFR ceilings into all three TAF sites between 08 and 12 UTC. Forecast soundings will take some time to saturate, so any precipitation will be in the form of light drizzle. && .OAX WATCHES/WARNINGS/ADVISORIES... NE...None. IA...None. && $$ SHORT TERM...Mayes LONG TERM...Mayes AVIATION...Fortin is the U.S. government's official web portal to all federal, state and local government web resources and services.