Area Forecast Discussion
Issued by NWS St. Louis, MO
Issued by NWS St. Louis, MO
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605 FXUS63 KLSX 110333 AFDLSX Area Forecast Discussion...Updated Aviation National Weather Service Saint Louis MO 1033 PM CDT Mon Jun 10 2024 .KEY MESSAGES... - Temperatures will trend higher Tuesday into Wednesday with above normal warmth favored from midweek onward. Widespread 90s could arrive by next weekend to bring the warmest air so far this year. - An active pattern to the north could bring a couple glancing rounds of showers and thunderstorms Thursday into next weekend. && .SHORT TERM... (Through Late Tuesday Night) Issued at 301 PM CDT Mon Jun 10 2024 A relatively quiet period is expected for a change with the primary focus being on warming temperatures. The synoptic overview shows surface high pressure straddling the U.S.-Canadian border and gliding into the Great Lakes Region this afternoon. Northerly surface flow is complimented by north-northwest flow aloft, resulting from a broad upper trough over the New England Region and mid/upper level ridging over the northern Plains and Upper Midwest. The pattern has supported refreshing, slightly-below- normal temperatures with mid to upper 70s accompanied by comfortable dewpoints in the low to mid-50s. The only caveat to the pleasant conditions is the scattered to overcast cloud cover that extends along a trough currently draped from north-central Missouri through east-central Missouri and southern Illinois. Cloud cover has held temperatures down a couple degrees versus areas in full sunshine. It has been inconsequential otherwise. As we progress through the remainder of the short term period, the eastward translation in the surface high and mid/upper ridge will lead to return flow at the surface. Warm air advection draws temperatures closer to the 80 degree along and west of the Mississippi River Tuesday. Cooler mid-level temperatures (8-10C) hang on long enough to the east that Illinois locations remain in the mid/upper 70s. It looks like yet another pleasant, early summer day with plenty of sunshine. Only scattered high clouds edge into central and northeast Missouri during the afternoon. A weak cold front attempts to push in late Tuesday, but latest guidance continues to show little moisture to work with and even suggests surface flow largely remains out of the west and southwest. It makes it difficult to say that it will have much more impact than a brief wind shift over northern sections of Missouri into west- central Illinois as it becomes west-east oriented and southward progress stalls. Meanwhile, 850mb temperatures continue to warm through midweek, rising into the upper teens Wednesday. Therefore, the main story will be the return to summer-like warmth with 60-70% of the grand ensemble members showing highs above 85. Though Warmth is not expected to be oppressive, there will be ever-so-gradual increase in moisture as dewpoints creep back into to the 60s from west to east. Maples && .LONG TERM... (Wednesday through Next Monday) Issued at 301 PM CDT Mon Jun 10 2024 There are a couple of chances for precipitation through the long term period. However, the inherent uncertainty with each round keeps warming temperatures the primary focus. An active, quasi-zonal pattern sets up over the northern Plains by midweek with upper level ridging building out of the southwest into the southern and central Plains. Several shortwaves are introduced into the northern periphery of the upper ridge, ejecting them into the Upper Mississippi River Valley late Wednesday and late Thursday. Unfortunately, this is a pattern that introduces a great deal of uncertainty with limitations on the placement and timing of resulting thunderstorm potential. Nonetheless, the first round looks to be well enough north (eastern Dakotas to northern Iowa) to avoid much in the way of thunderstorm as dying convection pushes east southeast around the upper ridge. A remnant shower cannot be entirely rule out in the pre-dawn hour early Thursday morning, but the potential is low given the surface to mid-level ridging that encompasses the eastern third of the Conus. Though Wednesday`s system isn`t expected to have much sensible impact, the track and evolution of the thunderstorm complex could very well determine the southward reinforcement of a slow- approaching cold front from the the north Thursday night into Friday. With the second shortwave just coming into view of the mid- range guidance, there are some discernible, unsurprising difference in the latitudinal placement of the shortwave and surface front. The general theme is for most convection to initiate somewhere north of the Missouri/Iowa border, focused around the better ascent in relation to the track of the upper wave. MUCAPE south of the west- east oriented front builds to around 3-4k J/k along the Missouri/Iowa border. Initial thoughts are than the CAPE gradient and west-northwest flow drives the bulk of convection through northern Illinois, while the trailing cold front slowly sinks southward into northern Missouri. While there is shower and thunderstorm potential along the front, confidence in thunderstorm intensity and overall southward spread remains low given the questions with the track of the shortwave and surface to mid-level height rises to the south. The boundary returns back to the north as a warm front as upper ridging continues to build in late this week. Isolated to scattered thunderstorms could line the front, but much of the upper support remains over the northern Plains into the Upper Midwest. The main story remain the temperature with the potential for widespread 90s by Sunday into early next week. Maples && .AVIATION... (For the 06z TAFs through 06z Tuesday Night) Issued at 1033 PM CDT Mon Jun 10 2024 Dry and VFR flight conditions will continue through the rest of the TAF period with light winds. Light and variable overnight winds will become southerly then southwesterly by Tuesday afternoon as surface high pressure shifts to the east. MMG/Glass && .LSX WATCHES/WARNINGS/ADVISORIES... MO...None. IL...None. && $$ WFO LSX