Area Forecast Discussion
Issued by NWS Indianapolis, IN
Issued by NWS Indianapolis, IN
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928 FXUS63 KIND 021745 AFDIND Area Forecast Discussion National Weather Service Indianapolis IN 145 PM EDT Thu May 2 2024 .KEY MESSAGES... - Warm and more humid today and tonight with chances for showers and thunderstorms. - Multiple chances for showers and storms throughout much of the forecast period, with continued above normal temperatures. - Repeated rounds of rainfall may lead to redevelopment of river flooding. && .MESOSCALE UPDATE... Issued at 144 PM EDT Thu May 2 2024 Latest surface observations show a warm front lifting northward across Indiana. Here in Indianapolis, surface dew points rose from 49 to 65 quickly after frontal passage. Concurrently, temperatures have risen into the lower 80s. Satellite imagery shows a cumulus field developing from the front southward, with the greatest concentration of cumulus developing over the more forested/elevated parts of central Indiana. ACARS soundings out of IND corroborate this, showing a substantial amount of low-level moistening and erosion of a weak capping inversion. However, this weak capping inversion remains as of 17z...located around 850mb. It can be seen in the characterization of the cumulus field, which is relatively flat at the moment. As the boundary layer warms, it is expected that this cap gradually dissipates over the next several hours. It`s at this point that we`ll begin to see the threat for isolated showers and storms, since lapse rates are quite a bit steeper above just above the cap. Model hodographs show a lack of shear through the depth of the column (some faster flow exists above the CAPE profile but storms may not reach high enough to feel the effects). With modest dry air in the soundings above 850mb it is possible that a few of the more robust updrafts produce gusty winds upon their collapse. Additionally, an isolated instance of hail is possible, but may be limited in size due to poor storm top venting and modest updraft strength. There are a few factors that should act to limit convection this afternoon. These include a lack of large-scale lift and advection of slightly drier air around the backside of a surface high to our east. As this process occurs, higher-res models tend to concentrate available buoyancy along and just south of the warm front. As such, any showers and storms would likely be nearer to this boundary compared to places further south. Overall, convective coverage will likely remain isolated and spread northward with time. && .FORECAST UPDATE... Issued at 1011 AM EDT Thu May 2 2024 No changes needed to the forecast this morning. Latest satellite shows diminishing cloud cover, which will set us up for a very warm day today. A northward moving warm front will lift across the region through morning and into the afternoon. An isolated shower or storm is possible, but probabilities remain low. We reduced the dew point a bit with the anticipation that mixing will be rather deep today. Expect near record highs in the mid to upper 80s. && .SHORT TERM (This afternoon through Friday)... Issued at 748 AM EDT Thu May 2 2024 Synopsis: Surface analysis early this morning shows two high pressure systems, one over the western Great Lakes, and a second over the Carolina`s. A cusp like feature was found across Central Indiana between these two highs, with light northeast winds in place mainly north of I-70, and light to calm winds across southern Central Indiana. Dew points on the north side of this cusp were dry, in the mid to upper 40s and low 50s. Across southern Central Indiana dew points were in the lower 60s. Deep and strong low pressure was found over the TX/OK panhandle and SW Kansas, along with a warm front that stretched north toward NB and IA. Abundant convection was found near these features. GOES16 shows mainly clear skies across Central Indiana. A dying thunderstorm/shower was found over southern IL and was drifting NW. Today... Models today show the low pressure system over the western plains pushing northeast toward IA through the day. This will result in the previously mentioned cusp like boundary to push to northern Indiana by this afternoon and allow the warmer and more humid air mass found across southern Indiana to return to Central Indiana. Aloft, ridging over the Appalachians is expected to strengthen, and this enhancement will allow for the development of southwest flow aloft into Central Indiana and weak broad lift. Little in the way of lower level forcing is available this afternoon, although our area will be within the warm sector. Forecast soundings show attainable convective temperatures this afternoon, with CAPE around 1400 J/KG and pwats around 1.15 inches. A cap does not appear to be in place. HRRR hints at some shower/storm development late this afternoon which given the warm and humid air mass in place seems reasonable. Will use a dry forecast until 18Z-20Z, there after include chance pops for precipitation given the diurnal heating and favorable air mass in place. Low confidence in specific timing and location. Given the expected time in the warm and humid air mass today, highs in the middle 80s appear on the mark. Tonight... Showers and storms will once again be possible tonight. Models suggest that as the IA surface low continues to progress northeast toward Ontario, an associated cold front will be dragged toward Indiana late overnight. Aloft ahead of the front, southwest flow is noted in place across Indiana and upper forcing appears present within that flow amid a shallow associated upper trough. Best timing appears to be from the late evening through the overnight hours. Forecast soundings trend toward saturation overnight with pwats near 1.50. HRRR suggests scattered showers/isolated thunderstorms passing across our forecast area overnight as these features pass. Thus given the upper forcing and the favorable air mass in place, confidence for precipitation tonight is high. After diurnal convection from the afternoon and early evening wanes, this more organized precipitation with upper forcing available will arrive. Thus a few hours in mid evening with no pops appear possible between these two types of forcing. Overall, will use high pops, mainly focused overnight when then upper forcing is expected to pass. Given the rain and the lack of wind shift through the night, lows only in the middle 60s are expected. && .LONG TERM (Friday night through Wednesday)... Issued at 748 AM EDT Thu May 2 2024 Friday and Friday Night... Look for the extended to remain warm with unsettled weather as daily rain/storm chances are in the forecast. Widespread convection will likely be ongoing to start the period on Friday due to increasing large scale ascent and moisture advection from an upper shortwave traversing the region. Organized convection is unlikely because of weak deep-layer shear, but sufficient instability should be in place for isolated to scattered storms. Latest guidance shows the best forcing for ascent will shift east late in the day leading to lower POPs heading into the overnight hours. Saturday through Sunday night... Uncertainty increases over the weekend with no substantial synoptic systems expected to impact central Indiana. While precipitation chances persist, the best chance for precipitation appears to be late Saturday as a weak cold front approaches. Most guidance suggest this frontal boundary will struggle to make much progress before stalling out over portions of the area. Abundant PBL moisture is likely to remain in place for this reason which supports keeping at least low POPs in the forecast through the weekend, especially during the afternoon hours when diurnal heating allows for better destabilization. POPs for Sunday may be lowered across the north in future updates depending on how far the front is expected to progress. Severe weather is unlikely due to weak deep-layer shear. Monday onward... Confidence in the forecast for this period remains relatively low due to diverging model solutions. However, ensemble guidance generally shows an unsettled weather pattern continuing with broad troughing over much of the CONUS. There is a signal for increasing instability/deep-layer shear which could lead to some severe weather threat materializing, primarily Tuesday into the middle of next week. CSU machine learning and CIPS analogs are both still suggesting the potential for strong to severe storms. While there is a signal, predictability is low this far out due to the large spread between models. Expect confidence to improve over the weekend into early next week once models become better aligned. && .AVIATION (18Z TAF Issuance)... Issued at 144 PM EDT Thu May 2 2024 Impacts: - Convection possible this afternoon and evening. - MVFR/IFR conditions possible in any convection that strikes a TAF site. - Confidence for afternoon showers/storms is low. - Confidence for overnight showers is high. Discussion: A warm front lifting northward across Indiana will allow winds to become southerly, occasionally gusting to 20kt this afternoon. Enough moisture and instability exists for a stray shower or thunderstorm during the afternoon as the front lifts northward. Coverage will be very widespread, and confidence that a shower/storm impacts a terminal is low. Will carry VCSH/VCTS during the most likely timeframe for this...should it occur. Any shower or storm may briefly reduce affected terminals into MVFR/IFR conditions. A more widespread area of showers and possibly a thunderstorm arrives late tonight. Confidence with this is much higher, and all terminals are expected to see rainfall and at least MVFR conditions. Low-level moisture and cloud cover could allow MVFR conditions to persist through much of the day on Friday. A cold front then arrives late Friday afternoon, switching winds to northwesterly and improving ceilings somewhat. && .IND WATCHES/WARNINGS/ADVISORIES...None. && $$ MESOSCALE...Eckhoff UPDATE...Eckhoff SHORT TERM...Puma LONG TERM...Melo AVIATION...Eckhoff