Area Forecast Discussion
Issued by NWS Indianapolis, IN
Issued by NWS Indianapolis, IN
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060 FXUS63 KIND 011315 AFDIND Area Forecast Discussion National Weather Service Indianapolis IN 915 AM EDT Mon Jul 1 2024 .KEY MESSAGES... - Continued cool with low humidity today - Heat and humidity returns on Tuesday and continues through Friday - Rain and thunderstorm chances Wednesday onward && .FORECAST UPDATE... - Sunny and Pleasant this afternoon Surface analysis late this morning shows strong high pressure in place over MI. Cool and dry easterly flow was in place over Central Indiana. GOES16 shows clear skies across Central Indiana, and dew points were mainly in the 50s. Aloft, water vapor imagery showed strong ridging in place over the plains states. This was resulting in NW flow aloft and subsidence over Indiana. ACARS soundings this morning show a very dry column with a sharp mid level inversion that will prevent any CU formation. Little overall change is expected through the day with this profile. Thus a mostly sunny sky will be expected as the high drifts to the eastern Great Lakes by this evening. The dry and easterly flow today will result in weak cold air advection today. However this should just result in persistence type highs, in the upper 70s. Overall, ongoing forecast remains in good shape. && .SHORT TERM (Today and tonight)... Issued at 220 AM EDT Mon Jul 1 2024 Mid-upper level ridge axis will remain west of Indiana today and winds will veer to easterly as the whole pattern progresses. This synoptic configuration will support one more day of relatively cool temperatures and low humidity. Periodic cirrus may be observed as high-level moisture crests the ridge. With a reasonable model spread on temperatures, a blended approach is acceptable. An increase at most locations by a degree or two compared to yesterday is expected. Radiative conditions will still be reasonably good for anomalously cool temperatures tonight, and have adjusted to raw and high resolution models that fall between about the 10th and 90th percentile. Low to mid 50s for minimums. && .LONG TERM (Tuesday through Sunday)... Issued at 220 AM EDT Mon Jul 1 2024 The synoptic scale pattern through the upcoming week won`t be too different than the last few weeks, with low-amplitude progressive shortwave troughs periodically passing. These may trend slightly more amplified than we`ve seen recently, but we`ll still be on the southern periphery of stronger westerlies aloft resulting in marginal shear and overall weak forcing for each precipitation event. As we saw yesterday, it`s difficult to accurately convey precision of convective timing and intensity in these type of patterns. One diurnal convective uptick can augment the upper flow pattern and influence mesoscale features in the subsequent diurnal maximum, essentially resulting in a domino effect causing model predictability to deteriorate with time. The good news is that the deterministic and ensemble suite of model guidance is in generally good agreement on individual shortwave trough timing and periods of stronger forcing for ascent in our region (albeit relatively weak as explained above). A lead wave that passes to our north early Tuesday and hastens the return of rich subtropical moisture to the higher latitudes, though still positioned to our west. Convection spawn by this wave should be relegated to the northern Great Lakes. Also, as the ridge axis passes, warm plume will advect in causing temperatures to return to about normal for early July (mid 80s). Later Tuesday, a more amplified shortwave trough and attendant surface cyclone and front will encourage convection centered on Iowa and Wisconsin. Longevity should be limited by narrow rich moisture plume seen in IVT and PWAT anomalies, and weak flow/shear south of subgeostrophic speed maxima over Michigan. Nevertheless, some weak convection or convective debris will probably reach central Indiana late Tuesday night into early Wednesday. On Wednesday, the broader shortwave trough over Ontario and slightly dampening Southeast ridge will result in an east-west placement of a weakly baroclinic front across central Indiana. Veered flow and a connection to rich subtropical moisture, combined with diurnal destabilization and frontal forcing should result in scattered to numerous thunderstorms. Stronger westerlies aloft remain to the north but there may be just enough shear for weakly organized multi- cell clusters, and a thermodynamic environment that could favor at least localized severe wind gusts. In a reasonable worst case scenario, more organized short line segments would be capable of some more sustained strong to damaging wind gusts. Thursday (July 4th) is where mesoscale uncertainties increase considerably. At the synoptic scale, multi-model ensemble mean shows continued weakening Southeast ridge and an upstream trough, which should result in the synoptic boundary still being present somewhere in our region. It could be shunted south if previous day convection is robust enough, refocusing diurnal convection closer to the Ohio River or into Kentucky. There could also be one or more MCS/MCVs to focus renewed more concentrated convective development somewhere across the region. Thus, our approach for now is an ensemble based mean precipitation probability approach which is fairly broad and accounts for a variety of mesoscale scenarios. It`s worth noting though that our partners in media and emergency management should communicate a potentially active day with regards to thunderstorms, and associated hazards including lightning and strong wind gusts being the primary threats. Friday may be a little more synoptically-driven with a closing midlevel low to our north, probably focusing most of the convection east of our area into Ohio. There is some uncertainty on this as ensemble spread grows larger at this time range. This could give a modest reprieve from humidity and lower thunderstorm chances into next weekend. && .AVIATION (12Z TAF Issuance)... Issued at 617 AM EDT Mon Jul 1 2024 Impacts: - None. Discussion: North-northeast winds early this morning will veer to more of an east-northeasterly direction by mid-morning. VFR conditions will prevail. && .IND WATCHES/WARNINGS/ADVISORIES... None. && $$ UPDATE...Puma SHORT TERM...BRB LONG TERM...BRB AVIATION...BRB