Area Forecast Discussion
Issued by NWS Indianapolis, IN
Issued by NWS Indianapolis, IN
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280 FXUS63 KIND 260149 AFDIND Area Forecast Discussion National Weather Service Indianapolis IN 949 PM EDT Wed Sep 25 2024 .KEY MESSAGES... - Partly to Mostly Cloudy Tonight and Thursday - Seasonable temperatures for much of this week with highs in the 70s and lows mostly in the mid 50s to mid 60s - Potential widespread beneficial rain Friday through Saturday from the combination of a cutoff upper low and the remnants of Helene - Gusty winds over 40mph possible Friday from the remnants of Helene && .FORECAST UPDATE... Issued at 932 PM EDT Wed Sep 25 2024 The upper trough over the area will continue to keep cloud cover across our forecast area overnight. The mid and high cloud can be seen streaming northward ahead of the trough axis from the lower Mississippi Valley. The trough axis has made minimal progress eastward this afternoon, keeping that similar flow in place tonight. This cloud cover will likely be more scattered over northern central Indiana, allowing for slightly greater diurnal cooling, but otherwise temperatures should be mostly in the upper 50s tomorrow morning. Grid updates are out. && .SHORT TERM (This evening through Thursday)... Issued at 300 PM EDT Wed Sep 25 2024 Synopsis: Surface analysis early this afternoon shows high pressure centered over the plains, nudging eastward toward the Ohio Valley. Low pressure was found over Lake Huron with an associated cold front stretching south through OH and eastern KY and eastern TN. Radar was quiet across central Indiana. Looking aloft, a highly amplified pattern was in place, with a large ridge over the western CONUS and a large upper trough stretching from the Great Lakes to the lower Mississippi valley. Models hinted at a cut off upper low over southern IL. All of this was resulting in cyclonic flow in place aloft over our region. GOES16 shows clear skies west of Indiana, however, abundant morning stratocu was burning off across Central Indiana leading to just some CU development and mid and high cloud streaming across Indiana due to the upper trough and low, pulling moisture northward. Tonight - Two weather features will control our weather tonight. The upper low over southern IL is expected to become more cut off from the upper trough and linger over western KY. This will continue to keep cyclonic flow in place aloft across the area tonight and into Thursday. Mid levels suggest the arrival of wrap around mid level moisture reaching Indiana overnight, particularly across the southern parts of the forecast area, including Vincennes, Bedford and Seymour. Northern extend of this moisture arrival appears a bit more limited. Our second weather feature will be the surface high pressure in place over the plains. This feature will be building eastward into Central Indiana, allowing drier surface air, dew points in the 50s, to build across the forecast area. Forecast soundings through tonight fail to show saturation. Thus with overall weak forcing in play, generally partly to mostly cloudy skies are expected. Expect the loss of any diurnal CU this evening, followed by the arrival of mid and high clouds due to the upper low overnight, particularly across the southern area. Given the clouds across the area and the lower dew point temps, lows overnight should reach the middle to upper 50s. Thursday - Little overall change is expected on Thursday. The upper low is expected to remain across western KY and western TN, while surface high pressure pushes to the Great Lakes. This will set up easterly lower level flow across central Indiana, with cyclonic flow aloft. Meanwhile Hurricane Helena will be pushing toward Florida, toward an eventual merge with the previously mentioned upper low. That transition looks to occur on Friday. Back to Thursday, the upper low and surface high pressure will again result in mid and high cloud steaming across central Indiana, especially south, within that cyclonic flow aloft, while the lower levels remain rather dry due to the easterly flow and high pressure. Forecast soundings for Thursday do suggest some afternoon CU will be possible. Thus once again, more partly to mostly cloudy weather. As there will be little change in the air mass, highs in the middle 70s, near persistence will be expected. && .LONG TERM (Thursday night through Wednesday)... Issued at 300 PM EDT Wed Sep 25 2024 The main focus in the long term period is the Friday through Saturday timeframe where the remnants of Hurricane Helene move into the Ohio and Tennessee Valleys, spreading rain and wind to portions of Central Indiana. The start of the period features a large upper low over the Ozarks with Hurricane Helene nearing the Big Bend of Florida. Guidance continues to be in fairly good agreement with the hurricane tracking northward through Georgia, then retrograding westward into Kentucky/Tennessee, then slowly meandering eastward through the weekend. Some uncertainty still remains regarding the northward extend of the track and precipitation shield associated with Helene. There likely will a south-north rainfall gradient across Indiana Friday through Saturday with the highest rainfall amounts further south toward the Ohio River. Latest ensemble guidance keeps the greatest chance of an inch of more of rainfall south of the I-70 corridor with potential rainfall amounts quickly diminishing north of there. In addition to the rain will be widespread gusty winds across the entire region Friday as the center of the transitioning extratropical Helene approach from the southeast. Tightening surface pressure gradient and a 40-50kt low level jet overhead may result in strong winds at the surface, with gusts over 40 mph possible early Friday morning through Friday evening. The wind threat will be watched closely over the next few days as headlines may be needed. Keeping 20-40 Pops through the weekend as the remnants of Helene remain in the area. Latest guidance keeps the upper low in the area through at least Sunday resulting in small waves of energy rotating into the region sparking off scattered showers. With such a moist column, extensive cloud cover should limit afternoon temperatures to the 70s and also not promote large diurnal temperature swings. So, look for overnight lows mostly in the 60s through at least the weekend. && .AVIATION (00Z TAF Issuance)... Issued at 948 PM EDT Wed Sep 25 2024 Impacts: - Increasing NE winds Thursday night Discussion: Any remaining MVFR cloud decks have eroded within a cooling boundary layer, leaving SCT to BKN 080-100, and 180-200 decks across the state. This should remain throughout the night with diurnal cloud increasing tomorrow afternoon around 5000ft. Winds have veered slightly towards N/NNE this evening, and will continue to veer towards NE tonight into tomorrow. With that said, winds will remain below 10kts through the next 24 hours mitigating impacts. However, Thursday night, a tightening pressure gradient out ahead of TS Helene will likely lead to increasing winds out of the NE, currently expected to be between 10-15ts. && .IND WATCHES/WARNINGS/ADVISORIES... None. && $$ UPDATE...Updike SHORT TERM...Puma LONG TERM...CM AVIATION...Updike