Area Forecast Discussion
Issued by NWS St. Louis, MO
Issued by NWS St. Louis, MO
Versions:
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
144 FXUS63 KLSX 061103 AFDLSX Area Forecast Discussion...Updated Aviation National Weather Service Saint Louis MO 603 AM CDT Sun Oct 6 2024 .KEY MESSAGES... - A cold front will move through the area today, resulting in steady cooling to near average temperatures by tomorrow afternoon. A gradual warming trend is expected Tuesday through the end of the week. - Gusty winds and low humidity will lead to more widespread elevated fire danger this afternoon, mainly in open grasslands and agricultural fields. This will be highly dependent on local fuel conditions. - There is very little potential for precipitation over the next week. && .SHORT TERM... (Through Late Monday Afternoon) Issued at 306 AM CDT Sun Oct 6 2024 Quiet conditions prevail throughout the region early this morning as we await the arrival of a cold front over the next few hours. This boundary is currently located across northwest Missouri and eastern Iowa, and will steadily march southeastward through the morning, clearing our area by mid afternoon. Behind this front, winds will switch to the northwest, and cold air advection will gradually increase throughout the day. While this will keep temperatures a bit cooler than yesterday, particularly north of I-70, the core of the post-frontal airmass will not arrive until overnight and tomorrow, and thus afternoon temperatures will likely remain above seasonal averages save for a few counties in northeast Missouri and west- central Illinois. Instead, the greatest impact this front will have will be on fire weather conditions, as the airmass behind it will be very dry. Upstream dewpoints across Iowa have fallen well into the 30s and 40s early this morning, and this will be the case during the afternoon in our area as heating and deep mixing commences. Meanwhile, breezy northwest winds are also expected in a few areas, and the combination of these two factors will lead to elevated fire weather conditions this afternoon. Please see the fire weather discussion below for more details. Overnight tonight, the surface pressure gradient will steadily weaken as surface high pressure sinks further into the area, and winds will weaken. Temperatures are likely to settle into the 40s to low 50s as a result. By tomorrow, this surface high will move further south, bringing with it the core of the post-frontal airmass. Even still, this airmass will be competing with clear skies and strong insolation, and temperatures are likely to climb to near seasonal averages, which is very near 70 degrees for this time of year. Even lighter winds and continued clear skies will result in even cooler temperatures overnight Monday, likely in the 40s area- wide with perhaps a few valleys dipping into the 30s. BRC && .LONG TERM... (Monday Night through Saturday) Issued at 306 AM CDT Sun Oct 6 2024 From Tuesday onward, a benign weather pattern is expected to develop that will result in a gradual warming trend and little to no opportunities for precipitation. Today`s cold front is expected to sink all the way to the Gulf of Mexico and remain there for several days and possibly longer, while surface high pressure remains draped across the Mississippi Valley. Meanwhile, developing tropical cyclone Milton is very likely to drift east across the central Gulf and into Florida through mid-week, maintaining east-northeast low level flow and further preventing rich moisture from returning northward. This will make precipitation very difficult to produce, and this is well represented in NBM/LREF ensemble members which are almost completely dry through the end of the week. Meanwhile, a large ridge of high pressure across the intermountain west will slowly inch eastward through the week, allowing for steady warming across the central plains and Mississippi Valley. Ensemble mean 850mb temperature anomalies are forecast to very slowly inch upwards throughout the week, reaching near the 90th percentile by late in the work week and perhaps even warmer over the weekend. Likewise, NBM surface temperatures are forecast to steadily climb through the week, reaching near 80 degrees by mid-week and perhaps slightly warmer by the weekend. With no obvious features like shortwaves or cold fronts currently forecast, ensemble spreads are also quite narrow all the way through Saturday. Late in the weekend, model guidance does hint at another cold front finally sinking into the region, but even this boundary does not currently produce a significant signal for precipitation, as the preceding airmass continues to be dry. However, we will need to keep an eye on fire weather concerns late in the week and over the weekend, as there are hints of developing southwest flow after what will very likely be nearly two weeks without any meaningful precipitation. BRC && .AVIATION... (For the 12z TAFs through 12z Monday Morning) Issued at 601 AM CDT Sun Oct 6 2024 VFR flight conditions can be expected today, with almost entirely clear skies. Northwest winds will be somewhat breezy throughout the day, with the most persistent and strongest winds expected at UIN. Winds will switch slightly to out of the north to northeast during the evening and overnight, and weaken significantly. Otherwise, no hazards are expected. BRC && .FIRE WEATHER... Issued at 257 PM CDT Fri Oct 4 2024 A broad area will observe elevated fire weather conditions today, although the actual threat of wildfires will be highly dependent on the state of local fuels. A cold front will steadily move through the area this morning, and behind this front humidity is expected to quickly drop. By early afternoon we will likely see humidity values falling to roughly 20 to 25 percent, with a few locations possibly touching 15 percent as well. Winds are also expected to be breezy, likely between 10 and 15 mph sustained with gusts to near 20 mph. However, wind speeds are not likely to reach much higher than this aside from perhaps a few sporadic gusts. Deep mixing to near 5000 ft will also promote efficient ventilation and smoke dispersion. These conditions will support erratic fire behavior in areas where fuels are receptive to burning, which remain highly variable. However, areas north of I-70 have seen no meaningful rainfall over the last week or more, and also have a high percentage of land that is predominantly covered by finer fuels like grasses, along with agricultural areas where the fall harvest is well underway. Agricultural fields with significant cover of cured crops or crop debris will be among the most vulnerable areas considering how quickly this vegetation dries out. BRC && .CLIMATE... Issued at 242 PM CDT Fri Oct 4 2024 Daily record highs for Saturday Oct 5 KSTL: 92 in 1938 KCOU: 94 in 1937 KUIN: 89 in 1938 && .LSX WATCHES/WARNINGS/ADVISORIES... MO...None. IL...None. && $$ WFO LSX