Area Forecast Discussion
Issued by NWS Indianapolis, IN
Issued by NWS Indianapolis, IN
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169 FXUS63 KIND 281859 AFDIND Area Forecast Discussion National Weather Service Indianapolis IN 259 PM EDT Fri Jun 28 2024 .KEY MESSAGES... - Rain showers/isolated thunderstorms overnight and early Saturday - Becoming partly sunny on Saturday afternoon. - Cooler Sunday and Monday, heat returns on Tuesday and Wednesday. - Rain/storm chances return Wednesday onward. && .SHORT TERM (This evening through Saturday)... Issued at 258 PM EDT Fri Jun 28 2024 Surface analysis early this afternoon shows strong high pressure centered over eastern NY and NJ. This high was influencing the weather across the eastern third of the country, including Indiana. The high was providing southeasterly to southerly flow across Central Indiana. Surface low pressure was found over NB. Warm and moist southerly flow was found streaming northward through the Mississippi river valley, where abundant cloud cover was found. This cloud cover was advecting east toward central Indiana. A large area of showers with a few thunderstorms were found over IA/Northern IL and MO. Water vapor imagery showed a mainly zonal flow in place across the CONUS, with a wave of moisture in place from the southern plains to middle Mississippi valley to the western Great Lakes. A short wave within this flow was found over SW MO. Dew points across central Indiana were mainly in the lower 60s. Tonight... Models suggest that within the upper flow several weak upper disturbances will pass across Indiana tonight and on early Saturday. Meanwhile within the lower levels the low pressure system over NB pushing toward the Great Lakes tonight dragging an elongated cold front across the Mississippi Valley toward Central Indiana. Forecast soundings this evening remain dry as these features approach. However the forecast soundings show deeper saturation arriving after 09Z with pwats near 2.25 inches. Instability appears quite limited as CAPE remains mainly below 500 J/KG. HRRR shows showers mainly arriving after 08Z, then passing into the forecast area by 12Z. Thus will have a dry forecast this evening, but begin ramping up pops overnight as the forcing and moisture begin to arrive in the area. Confidence for rain is high. Given the expected clouds and precipitation and the cold front not passing until after 12Z expect lows in the lower 70s, with some middle 70s south. Saturday... Models suggest that at 12Z forcing and the associated cold front will be over Central Indiana. This should then continue to exit to the east through the morning hours on Saturday, with the focus mainly along and south of an I-70 line. By 18Z, forecast soundings lose their deep saturation and winds become westerly in the wake of the cold front. Aloft forcing is lost as it pushes east by the afternoon. Again, instability appears limited as little CAPE is available, however a stray thunderstorm cannot be ruled out. Thus will continue high pops through the morning hours, mainly across the southern half of the forecast area and trend toward a dry forecast by afternoon. Minimal overall temperature advection is expected until Saturday night. This will lead to a quick recovery of high temperatures on Saturday afternoon to the middle 80s. && .LONG TERM (Saturday night through Friday)... Issued at 258 PM EDT Fri Jun 28 2024 Generally quiet weather through much of the long range as broad ridging takes hold early next week. Rain chances return late in the period. Saturday Night and Sunday Any lingering showers from Saturday`s cold front / shortwave will be slowly exiting the area by Sunday morning. Much cooler conditions will follow, as surface high pressure builds in from the north. Model temperatures in the 850mb level drop to around 11C in most guidance, with some members showing as low as 8C by Sunday night. Around the same time, the surface high moves directly overhead with large-scale subsidence. Clear skies, light winds, and a cold air mass should promote temperatures well-below normal Sunday night into Monday morning. Lows should drop well into the 50s with perhaps some rural areas dropping into the 40s. Normal lows are around 65 for this time of the year. Monday Onward Cooler than average temperatures linger into Monday with highs climbing into the 70s for the most part. A few locations may reach 80, especially further south away from the core of the now-departing cold air mass. As high pressure slides eastward, low-level flow turns southerly and a warming trend looks to commence. By Tuesday, 850mb temps rise by about 5-10 degrees, which under full sun and efficient mixing corresponds to highs in the mid to upper 80s. The primary axis of warm air advection remains to our west, however. This warm air advection enables a ridge to build over the Plains which then drifts eastward through the week. As such, generally above-normal temps in the upper 80s / low 90s should persist through the remainder of the week. Low temps should also be a bit above normal, reading in the high 60s to low 70s for most locations. Turning our attention to precipitation chances, we`ll see quiet weather associated with high pressure persisting through Tuesday. Most guidance shows a cold front attempting to infiltrate the aforementioned ridge by Wednesday night or Thursday. This front combined with increasing humidity from the south could allow for repeated shower/storm chances. Ensemble guidance shows the ridge axis moving eastward a bit allowing flow to be south/southwesterly through the column across Indiana. Since the front is diving down from the northwest and encountering largely boundary-parallel flow...most guidance stalls the front somewhere nearby (most show central or southern Indiana). Shower and storm chances could then linger through the rest of the week if this is the case. Ensemble guidance is in fairly good agreement through Wednesday but diverges thereafter. And this is probably due to how individual members handle the front impinging on the departing ridge. Therefore, confidence in forecast temperatures and precipitation decreases by late Thursday and Friday. && .AVIATION (18Z TAF Issuance)... Issued at 1215 PM EDT Fri Jun 28 2024 Impacts: - VFR expected for much of the TAF period. - Showers with isolated TSRA possible after 07Z. Discussion: Clouds over IL and MO will continue to increase and thicken this afternoon, however cigs will remain VFR through most of the period. Low pressure over NB is expected to advance northeast and push a cold front across Central Indiana late tonight and early Saturday morning. Forecast soundings suggest a nearly saturated column as the front approaches and passes through Central Indiana. HRRR also shows an area of showers passing with the approaching dynamics and cold front overnight and early on Saturday. Thus confidence is high for showers passing across Central Indiana late tonight and early on Saturday, however confidence on specific timing and locations is low. Thus will include a large window of VCSH late tonight. Have used a tempo group on Saturday morning as the best forcing is expected to pass. Although a thunderstorm will be possible, the time of day and limited instability are unfavorable for convection. For now have left thunder out due to low confidence. && .IND WATCHES/WARNINGS/ADVISORIES...None. && $$ SHORT TERM...Puma LONG TERM...Eckhoff AVIATION...Puma