Area Forecast Discussion
Issued by NWS Indianapolis, IN
Issued by NWS Indianapolis, IN
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217 FXUS63 KIND 131349 AFDIND Area Forecast Discussion National Weather Service Indianapolis IN 949 AM EDT Thu Jun 13 2024 .KEY MESSAGES... - Warming trend continues today with highs near 90F. - Thunderstorms possible this evening into tonight...with possibly a few strong/severe cells north of I-70. - Hot and humid trend starts Sunday. && .FORECAST UPDATE... Issued at 948 AM EDT Thu Jun 13 2024 The forecast remains in good shape with only minor adjustments needed to match observations. Current satellite imagery shows mostly clear skies across central IN as surface ridging remains in place. Expect quiet weather conditions to persist for much of today before a complex of storms begins to approach this evening. More details on the potential for storms is provided in the short term discussion. Additional updates on thoughts for timing and the threat of damaging wind gusts or severe hail will be sent out in the afternoon forecast package. Increasing southerly flow and plentiful sunshine will lead to warmer temperatures in the upper 80s to possibly low 90s in a few spots. Today will likely end up being the warmest day of the day so far. Thankfully dewpoints are going to remain in the 50s for most locations so heat indices should remain below 90F. Still make sure to stay hydrated and take breaks if you are outdoors this afternoon as it will be hot. && .SHORT TERM (Today and tonight)... Issued at 304 AM EDT Thu Jun 13 2024 Our primary forecast challenge in the short term is convective activity arriving around 00z this evening. WINDS and TEMPERATURES A shortwave and associated cold front are approaching from the northwest. The shortwave itself looks to pass to our north, but the cold front sags southward and should arrive early Friday morning. Warm southwesterly winds could gust up to 20mph today as the MSLP gradient tightens ahead of the approaching front. In addition to storm chances, the front will lead to a brief cool down in a pattern that favors continued warming. Winds turn northwesterly after frontal passage and colder air gradually filters into the region. Though Friday may be a bit cooler, it shouldn`t be that much cooler...only a few degrees at most with highs in the mid 80s as opposed to near 90 today. Lows Friday night may bottom out near 60 across our northern counties and in sheltered areas or valleys elsewhere. Temporarily reduced temperatures continue into Saturday as well with highs in the mid to upper 80s. CONVECTIVE POTENTIAL AND HAZARDS Guidance is in fairly good agreement showing convective activity igniting along the front across SE Iowa and northern Illinois. These storms should organize into a cluster given high DCAPE and potential for efficient cold pool generation/growth. Shear vectors are not boundary-parallel, however, so initial activity may remain discrete for a few hours before upscale growth occurs. This may also negate system longevity with southeastward extent as cold pool shear balance will be harder to achieve. Any resulting MCS may quickly become outflow dominant as it heads into our CWA from the northwest. Additionally, model CAPE diminishes quite quickly as one heads south and east through central Indiana. This all points to a weakening system as it moves through central Indiana. In terms of hazards, strong to severe wind gusts are most likely. The greatest potential being further northwest where storms are strongest. Severe potential diminishes quickly as one heads south and east. Still, anywhere from Terre Haute, to Indianapolis, to Muncie may see a strong wind gust as thunderstorms move through. Storm timing again looks to be this evening, around 00z near Lafayette, to as late as 04z by Bloomington. There remains some variation within guidance but most are within this range. Timing also depends a bit on convective evolution and how quickly upscale growth occurs. Lingering rain/cloud cover may hold on to as late as 12z in the MCS`s wake. && .LONG TERM (Friday through Wednesday)... Issued at 304 AM EDT Thu Jun 13 2024 The primary forecast challenge in the long term is heat and associated heat related hazards. SYNOPTIC OVERVIEW Guidance is in good agreement showing a trend towards east coast ridging and southwesterly surface flow across Indiana. In a nut shell, this means a warming trend appears likely. But how much warming? Ensemble guidance shows rather anomalous ridging from Sunday onward. In fact, both the NAEFS and ECMWF ensembles show 99th (or higher) percentile height anomalies at 200b and 500mb. The ridge depicted within guidance is broad, stretching from the Plains into the northeastern US and even into the Atlantic Ocean. The deterministic ECMWF shows 600dm heights by mid-week centered over Indiana. Beyond next week, ensemble guidance diverges and shows little to no coherent signal. As such, little can be discerned synoptically in the 8-14 period. But sustained ridging into the end of June does not appear as likely by this point, and a trend back towards normal weather is favored. PRECIPITATION While a strong ridge favors above to much above normal temperatures, precipitation anomalies can be a bit more of a challenge. Guidance shows sustained moisture advection from the gulf around the western edge of an east coast surface high. This may lead to "air mass" thunderstorms at times once the ridge and heat really settle in. Additionally, decaying cold fronts may occasionally dip far enough south to initiate some convection. However, this may not materialize as the jet stream looks to be far north across Canada. The synoptic storm track may be simply too far away to bring a front this far south. This depends on how amplified the ridge becomes. Coincident with this analysis, CPC 6-10 and 8-14 day outlooks favor warmer than normal conditions and near-average precipitation. We will carry slight chance PoPs at times from Tuesday onward to account for pop up afternoon convective potential within the core of the ridge. TEMPERATURES Guidance is in good agreement showing highs reaching at least 90 most of next week. A limiting factor regarding max temperature potential is moisture advecting from the south. Dew points look to be high most of next week, with readings 65 to 75 likely much of the time. This moisture may limit the depth of boundary layer mixing and therefore max temperature potential. However, it also has the effect of raising the heat index to potentially excessive levels. The NWS Heat Risk tool shows major to extreme heat risk for much of the area Monday onward. Multi-day prolonged heat potential with little overnight relief adds to the risk by mid to late week. && .AVIATION (12Z TAF Issuance)... Issued at 648 AM EDT Thu Jun 13 2024 Impacts: - Thunderstorms arriving after about 00z this evening. - Lingering MVFR ceilings in the wake of shower/storm activity. Discussion: VFR conditions expected through the afternoon. Generally southwesterly winds with occasional gusts 15-20 knots can be expected. A cold front approaching from the northwest will trigger thunderstorms across northern Illinois late this afternoon. These storms should progress southeastward into Indiana. The main forecast challenge will be storm intensity, as most guidance shows weakening with time and southward extent. Still, nearly all members of guidance depict shower/storm activity affecting all terminals. Will include a tempo group for thunderstorm at LAF, IND and HUF, where greater intensity storms may occur. Will mention VCTS south at BMG where weakening allows for a bit more ambiguity in terms of impacts. Showers/storms should be mostly out of the area between 08-12z. Lingering MVFR ceilings are possible in the wake of the storm complex but should begin to clear up Friday afternoon. && .IND WATCHES/WARNINGS/ADVISORIES... None. && $$ UPDATE...Melo SHORT TERM...Eckhoff LONG TERM...Eckhoff AVIATION...Eckhoff