Area Forecast Discussion
Issued by NWS Indianapolis, IN
Issued by NWS Indianapolis, IN
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675 FXUS63 KIND 270500 AFDIND Area Forecast Discussion National Weather Service Indianapolis IN 100 AM EDT Fri Sep 27 2024 .KEY MESSAGES... - Strong northeast winds with gusts of 40-55 MPH expected late Friday morning through Friday evening. - Sporadic gusts above 55 mph possible Friday evening. - Widespread rainfall expected late tonight into the weekend with rainfall totals around 1-2 inches south of I-70. Locally higher amounts possible. - River flooding is not expected due to abnormally dry soil, but efficient rainfall rates may lead to localized flash flooding. && .FORECAST UPDATE... Issued at 959 PM EDT Thu Sep 26 2024 Hurricane Helene will make landfall along the Florida Gulf coast tonight and continue its fast northward pace into the Deep South, reaching the Atlanta area around dawn. Meanwhile a mid-latitude, rather small cut-off mid-level trough will continue to spin near the Tennessee-Mississippi border. The dumbbell motion between these two cyclones will have the baroclinic circulation direct the tropical storm in a curling formation towards the Ohio Valley...with its associated anomalous precipitable water reaching counties south of Interstate 70 by 12z. Therefore, expect rain chances and coverage to steadily increase in a SSE to NNW trend tonight...with rain likely over all central and southern zones by sunrise. Embedded heavy rainfall rates are expected at times along/south of the I-70 corridor after 6Z...with greatest coverage/frequency closer to the Ohio Valley. No flooding concerns at least through tonight with overall antecedent dry soils and rainfall through dawn likely only 0.25-0.75 inches across the region`s southern half. Winds will increase as well as the tropical circulation screams northward through Georgia. Sustained winds by dawn will be 15-20 mph for most locations, with gusts around 30 mph. The storm`s approaching track will promote small changes in wind direction, with a predominant northeast flow. Wind Advisory is still set to go in effect at 1000A Friday/later across central Indiana. Overnight minimums in the low to mid-60s will be the rule amid a subtle increase in surface dewpoints. && .SHORT TERM (This evening through Friday)... Issued at 258 PM EDT Thu Sep 26 2024 Strong winds and heavy rain from the remnants of Hurricane Helene expected much of the day Friday for Central Indiana. Latest satellite imagery shows Hurricane Helene pushing northward toward the Big Bend of Florida while clouds and deep moisture advection advect northward up the Appalachians and to the Canadian border. The earliest effects of the hurricane will begin to be felt across central Indiana as early as tonight as the potent tropical cyclone makes landfall along the Big Bend Coast of Florida. Helene will rapidly proceeds inland toward north Georgia and the Tennessee Valley by daybreak tomorrow. As Helene interacts with the large upper low over the Mid Mississippi Valley tomorrow, it will retrograde into the Ohio Valley. As this occurs, warm air advection aloft, strong winds, deeper moisture and more expansive cloud cover will push northwestward into the area tonight and through the day tomorrow. Wind Threat: The most impactful threat from the remnants of Helene locally will be strong winds across the state of Indiana. As Hurricane Helene transitions into an extratropical system and pushes toward the Ohio Valley, a strong 60-75kt low level jet develops on the northwest side of the system and moves overhead by Friday afternoon. In addition to this, pressure falls from around 1008mb to near 996mb through the day and an increasing pressure gradient will result in strong northeast winds Friday morning through Friday evening. Winds should steadily increase tonight with gusts at or above 40 mph increasing from SE to NW late morning. Strongest winds are expected within the 3pm-8pm timeframe where sporadic gusts to 60 mph will be possible. One caveat to the forecast is that the atmospheric profile will be largely saturated with weaker low level lapse rates, inhibiting much stronger LLJ winds from mixing down to the surface. For this reason, a Wind Advisory has been issued for all of Central Indiana with frequent gusts of 40-55mph expected. With how strong and dynamic this system is, gusts over 60 mph are not out of the question and still could happen; however they should be sporadic in nature. Another thing to note, strong winds out of the NE are not very common, potentially resulting in more impacts and down trees than one would expect from winds of this strength. Rainfall: Strong moisture advection will overspread the region as the Hurricane makes its way northward toward the region tonight. While the main area of low pressure is expected to remain south of the Ohio River, an expanding precipitation shield is expected to develop as the system becomes extratropical bringing heavy rain to portions of the state. Greatest moisture advection and PW will be further south with a sharp S-N gradient across the state. Best chance for rainfall amounts at or above 1 inch will be along and south of I-70 with lower values further north. Despite a long duration rainfall event, recent dry conditions and low river levels should prevent a widespread flooding event across the region. Localized flooding is possible, mainly across Southern portions of Indiana where heaviest rain rates and higher amounts are expected, but again, flooding is not a huge concern due to ongoing drought conditions. && .LONG TERM (Friday night through Thursday)... Issued at 258 PM EDT Thu Sep 26 2024 The main concern in the extended will be early in the period as the remnants of Helene linger near central Indiana. The strong wind gust and heavy rain threat mentioned in the short term is expected to continue through Friday evening before diminishing overnight. The remnant surface low from Helene should phase with an upper low and continue to gradually weaken through the weekend. Sufficient forcing and moisture will likely still be in place to support numerous showers through Sunday. Flash flooding appears unlikely over the weekend due to less efficient rainfall rates so the additional rainfall is welcomed news given the active drought conditions. However, a low end threat for localized flooding continuing into Saturday cannot be ruled out depending on the evolution or location of the system. The remnant disturbance begins to depart sometime late Sunday into Monday as mid-upper level ridging builds in ahead of an approaching trough. In the low-levels, lingering moisture will keep the potential for some diurnal showers in the forecast to start the work week. Weaker forcing and less available moisture may tend to limit the coverage of showers. By Tuesday, diverging model solutions leads to some uncertainty though ensemble guidance generally shows a deep trough and associated cold front approaching central Indiana. Limited moisture ahead of the front and weak overall forcing will once again limit chances for precipitation with only isolated showers expected. High pressure should then build in behind the front midweek providing quiet weather. Precipitation and clouds will limit diurnal temperature swings over the weekend with near seasonal highs. Temperatures remain near seasonal into next week, but a slight cooldown is likely behind the cold front. Look for highs in the upper 60s to low 70s by Wednesday and lows around the upper 40s to near 50F. && .AVIATION (06Z TAF Issuance)... Issued at 100 AM EDT Fri Sep 27 2024 Impacts: - Ceilings falling into MVFR category through early morning, IFR possible at times after daybreak - Rain expanding into the region through the morning - Significant aviation impacts from mid afternoon into the evening with heavier rainfall and wind gusts in excess of 40-45kts Discussion: Light rain and MVFR stratus is steadily expanding into the region from the southeast early this morning ahead of Helene which made landfall on the Florida panhandle a short time ago. Northeast wind gusts have been steady at 20-25kts but expect this to only increase as we near daybreak into the morning. Rain will also become widespread through the morning before briefly diminishing in coverage midday. Ceilings may dip to IFR levels during the morning...especially at KBMG and possibly at KIND. The greatest impacts to aviators will come by mid afternoon into the evening as the main remnants of Helene lift up into the region. Model guidance remains consistent on bring a swath of 70kt winds at 850mb around the northern flank of the remnant low and across the southern half of central Indiana. Despite poor lapse rates...this will likely translate to a 3-5 hour period with wind gusts in excess of 40-45kts and perhaps higher. The heaviest rain in the forecast period will come during this timeframe as well with IFR conditions likely. There is potential for a brief period of low level wind shear considering the very strong winds within the boundary layer. Wind gusts will begin to drop back by mid to late evening with rain lightening up as well. Gusts will drop further tonight into early Saturday. && .IND WATCHES/WARNINGS/ADVISORIES... Wind Advisory from 1 PM this afternoon to 11 PM EDT this evening for INZ021-028>031-035>038-043-044. Wind Advisory from 10 AM this morning to 9 PM EDT this evening for INZ039>042-045>049-051>057-060>065-067>072. && $$ UPDATE...AGM SHORT TERM...CM LONG TERM...Melo AVIATION...Ryan