344 FXUS63 KIND 071651 AFDIND Area Forecast Discussion National Weather Service Indianapolis IN 1151 AM EST Thu Feb 7 2019 .UPDATE... The AVIATION Section has been updated below. && .SYNOPSIS... Issued at 321 AM EST Thu Feb 7 2019 Heavy rain and the potential for a few severe storms are expected today ahead of a powerful cold front set to pass through the region late today into this evening. Gusty winds and rapidly falling temperatures will follow tonight in the wake of the frontal passage. Dry and much colder weather returns Friday through the first part of the weekend...but a storm system will bring the return of an unsettled pattern Sunday into the middle of next week. The first system will bring the potential for light snow accumulations Sunday and Monday. A second and stronger storm system will impact the Ohio Valley for Tuesday with rain...possibly changing back to snow Tuesday night and Wednesday as colder air returns. && .NEAR TERM /Rest of Today/... Issued at 1000 AM EST Thu Feb 7 2019 Some fog remains across central Indiana as well as lower visibilities due to rain and storms, but dense fog has ended and allowed the dense fog advisory to expire at 8 am. Heavy rain threat will continue through the day, with some isolated severe storms possible but widespread threat for severe looks less likely given all the rain inhibiting development of instability. Previous discussion follows... Central Indiana set to see a bit of everything over the next 18 hours or so in what very much feels like the proverbial kitchen sink getting chucked at us. Amplified upper level trough will swing east out of the northern Rockies eventually intensifying by tonight as it tracks into the upper Midwest. At the surface...the warm front over the lower Ohio Valley this morning will lift north through the area in response to a strengthening low pressure system lifting out of the southern PLains this morning. This system will track into the Great Lakes by late day and pull a powerful cold front through the area by early evening. Heavy rain and flooding...storms and a conditional severe threat...fog...gusty winds and the onset of a rapid temperature tumble will all occur between now and early this evening courtesy of this strong and multifaceted storm system. We will start with the fog which was touched on above. Fog will be most prevalent over the next 4 to 6 hours with the light wind flow...sharp and shallow inversion with warm air advecting into the region above the inversion. All in all...a classic setup for widespread dense fog. The most widespread fog exists over the southern half of the forecast area with more isolated pockets of dense fog further north. Decided however to issue the advisory for the entire area as expect more widespread dense fog will spread north over the next few hours as the warm front lifts out of the lower Ohio Valley. Suspect as more substantial rainfall and convection arrive from the southwest in the 09-11Z timeframe... should begin to see improvements in visibilities. Can always cancel the advisory early if need be but feel comfortable running the headline through 13Z. Shifting to primary concerns for today...another round of heavy rainfall poised to impact the region which will only further exacerbate ongoing flooding and potentially worsen it in some areas. In addition...the convective threat has grown with a narrow window for severe storms from late morning through mid/late afternoon. Model consensus developing a dual moisture fetch of Pacific and Gulf origin over the next few hours as the surface wave pulls out of north Texas and intensifies as it interacts with the strong jet aloft. This low level jet will only strengthen through the day and serve to advect a rich moisture surge into the Ohio Valley with the potential for precip water values to peak near 1.50 inches by this afternoon...above climatological peaks for early February and at 400- 500% of normal. With the unusually high moisture levels...deep low level convergence and diffluence aloft as the upper jet approaches...all signs point to waves of heavy and efficient rainfall until the cold front can pass late day. The addition of a convective component as well only accentuates the heavy rainfall concern. Much of central Indiana is likely to see another 1-2 inches of rain in addition to what has already fallen since Tuesday evening. The heaviest axis of rainfall should focus near and south of I-70 and think some areas may see locally higher amounts than 2 inches if any convective training sets up. Already plenty of flooding ongoing and with our ground absolutely saturated...runoff rates will increase and only worsen ongoing flooding. Flood Watch will continue in its current state today. There are also growing signals that central Indiana will have to contend with the first round of strong to severe convection for 2019 later today as parameters align for about a 3-5 hour window where severe potential is amplified. As the warm front surges through the area this morning...an area of elevated instability will follow with ongoing convection over the lower Ohio Valley increasing across the forecast area. As the region slides into the warm sector near and south of the warm front by mid to late morning...the arrival of the strengthening low level jet into the region will set the stage for an increasing damaging wind threat with any low topped convection continuing through about 20-21Z. Soundings noting wind speeds increasing to near 70kts if not a touch higher as low as 3kft by which even shallow convection should be able to tap into and pull a fair amount to the surface. While the damaging winds remain the primary severe weather concern...presence of the retreating warm front interacting with weak instability and a surge of higher helicities supports a small tornado threat into the afternoon as well. Best potential looks to be primarily over the Wabash Valley where there parameters align the best with the core of the strongest low level winds overhead. Think any conditional severe potential is over by 21Z or so as better moisture and stronger part of the low level jet shift off to the northeast. Cold front will lag the stronger convection by 1-3 hours...passing across the area closer to sunset and just after. Once the front passes...the onset of immediate and intense cold advection will lead to rapidly falling temperatures and an uptick in wind gusts. Temps...expect much of the area to make a run at the lower 60s with possibly mid 60s south prior to the cold front passing late afternoon and early evening. The warmer MAVMOS was largely a better fit for highs in most areas. && .SHORT TERM /Tonight through Saturday Night/... Issued at 321 AM EST Thu Feb 7 2019 Forecast challenges turn to gusty winds and falling temperatures tonight and a return of much colder air throughout the short term. The front will be clear of the forecast area by 00Z tonight with focus shifting to the falling temperatures and gusty gradient flow as mentioned above courtesy of cold advection and as strong surface pressure gradient. Equivalent potential temp profiles go vertical for into the early overnight as well. which would aid in getting stronger boundary layer flow to ground level for several hours. Expect peak wind gusts to periodically approach 40 mph for several hours Thursday night. Will highlight this threat in the HWO and pass onto the dayshift to determine if a Wind Advisory may be warranted tonight. One impact that may need to be considered for the Friday morning commute is the potential for a flash freeze as temperatures drop 40- 45 degrees from cold frontal passage late Thursday to daybreak Friday. The gusty winds may help to mitigate this concern somewhat and dry surfaces...but this will be something to monitor. May also see a very brief period with a few snowflakes on the back end of the precip shield this evening but this will have no impact. A strong area of high pressure approaching 1050mb will expand across the area from the Canadian prairies for Friday and Saturday with dry and much colder air returning. Expect plenty of sunshine and a continuation of gusty flow as the pressure gradient remains tight. Winds will relax Friday night as the core of the high moves into the region. Mainly clear conditions will continue through much of the rest of the forecast period as the Ohio Valley remains under the influence of the strong high pressure. Clouds will increase late Saturday night ahead of the next system poised to impact the region. Temps...the temperature changes from late Thursday afternoon to daybreak Friday are very impressive. Locations that warm into the lower 60s will be in the teens barely 12-15 hours later. Much colder air remains for the rest of the period with highs Friday and Saturday mainly in the 20s. Lows Friday night will drop into the single digits. An overall model blend worked reasonable through the short term. Subzero wind chills are possible for some late tonight through Friday night. && .LONG TERM /Sunday through Wednesday/... Issued at 227 AM EST Thu Feb 7 2019 Ensembles are in good agreement overall on the main weather pattern during this period. Upper ridging initially over the area will shift off to the east, as a significant trough ejects into the Great Lakes towards the middle of next week. Pattern looks unsettled for most of the extended, as periodic waves eject out of approaching western trough, with the strongest wave progged to arrive around Tuesday. Ensembles continue to suggest precipitation chances from Sunday through Tuesday in association with these waves, but differences in timing continue. Will continue with PoPs from Sunday through Tuesday to cover these potential waves. Ensembles still indicate potential for mixed precipitation and light accumulations of snow over parts of the area at times from Sunday through Monday night. By Tuesday, it appears enough warm air will get drawn into the area ahead of the strong short wave trough for rain by Tuesday. && .AVIATION /Discussion for 071800z TAF issuance/... Issued at 1141 AM EST Thu Feb 7 2019 Thunderstorm potential will continue at all but KLAF for the next few hours before moving off to the east. LLWS potential during that time as well due to a low level jet. Ceilings will continue to be low and then do some bouncing before dropping again. Cold front (currently across central Illinois at 17z) will pass through from northwest to southeast this evening. Winds behind the front will pick up out of the northwest and could see gusts of 30 to 35 kts with that. Could see VFR late during the overnight hours, but not high confidence. && .IND WATCHES/WARNINGS/ADVISORIES... Flood Watch through late tonight for INZ039>042-045>049-051>057- 060>065-067>072. && $$ SYNOPSIS...Ryan NEAR TERM...Ryan/CP SHORT TERM...Ryan LONG TERM....JAS AVIATION...CP