Area Forecast Discussion
Issued by NWS Indianapolis, IN

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783 FXUS63 KIND 302309 AFDIND Area Forecast Discussion National Weather Service Indianapolis IN 709 PM EDT Sun Apr 30 2017 .UPDATE... The AVIATION Section has been updated below. && .SYNOPSIS... Issued at 256 PM EDT Sun Apr 30 2017 A potent cold front will move through the area tonight, bringing more potentially heavy rain and strong to severe thunderstorms. Much cooler air will then move in for the work week. Windy conditions can be expected Monday and Tuesday. A low pressure system will bring more rain chances Wednesday into Saturday. && .NEAR TERM.../Rest of This Afternoon and Tonight/ Issued at 256 PM EDT Sun Apr 30 2017 Waves of showers and thunderstorms will continue to move through central Indiana this afternoon with continued isentropic lift in the warm sector of a low pressure system. There could be some strong to severe storms, especially east where better instability exists. However, heavy rain will continue to be the main threat with very high precipitable water values and a saturated ground. Tonight a final round of showers and thunderstorms will develop along a cold front and move through the area during the evening and overnight. Heavy rain will continue to be the main threat, but again some strong to severe storms are possible. Rain should exit the area by the end of the tonight period. The model blend looks good for temperatures given the expected conditions. Winds will be gusty at times tonight as some of the stronger winds aloft try to mix down, but expect gusts outside of storms to remain around 30 mph or less. && .SHORT TERM.../Monday through Wednesday/ Issued at 256 PM EDT Sun Apr 30 2017 Models are close enough that the model blend initialization was accepted for most items. There may be some partly cloudy skies Monday morning as the area is in the dry slot behind the cold front. However, during the afternoon wrap-around moisture will move in along with colder air aloft, allowing skies to become mostly cloudy. Along with the moisture return, some weak forcing could lead to a few showers, so went with some low PoPs during the afternoon. Colder air will flow in with highs only expected to be in the 50s most areas. However it will feel cooler thanks to windy conditions. A tight pressure gradient and cold advection will allow sustained winds over 20mph and wind gusts approaching 40 mph. These are below wind advisory criteria but are close. Will have to keep a close eye for a need to go with an advisory if expected speeds increase a little more. Cyclonic flow continues Monday night along with a surface trough moving through. This will provide enough forcing to go with some low PoPs most areas. Breezy conditions will continue. On Tuesday high pressure and drier air will try and build in from the west, and this will allow dry conditions and some sunshine to return. However the pressure gradient will still be tight enough for breezy conditions. Another upper trough will approach the area on Tuesday night and Wednesday. An area of convergence will set up across southern Indiana. These should provide enough forcing for some chance PoPs across much of the area by Wednesday afternoon. Stayed with the model blend for temperatures. These will be below normal, especially Wednesday when highs will only be in the 50s. && .LONG TERM /Wednesday night through Sunday/... Issued at 230 PM EDT Sun Apr 30 2017 Models and ensembles in general agreement that the long term will start off with a Plains trough and a weak eastern ridge. Then, an upper low will break off and move into the Tennessee Valley before being absorbed again by an Ontario low within the upper trough as the trough moves into the Appalachians. However, the 12z GFS briefly stalls the Tennessee Valley upper low Thursday night and thus is on the slow side of the ensemble means and even more so the 00z ECMWF by 12z Friday. However, the GFS is not as slow as the 06z or 00z versions. So, will lean toward a quicker ensemble mix. A southern Plains surface system will move across the Tennessee Valley Wednesday night and Thursday and the Appalachians Thursday night and Friday. Deepening moisture and isentropic lift should result in widespread showers with the potential for more heavy rain Wednesday night into Thursday. Then, should only see a few lingering light showers for the remainder of the work week. MOS blend temperatures look to have a good handle on the cool airmass that will be in place along with the extensive cloud cover that is expected to be around starting Wednesday night. The result will be well below normal temperatures with highs only in the 50s on Thursday. As the system exits northeast, should see some sunshine and moderating weekend temperatures. && .AVIATION /Discussion for 010000Z TAF Issuance/... Issued at 709 PM EDT Sun Apr 30 2017 Restrictions expected within rain and storms tonight otherwise VFR conditions through late afternoon Monday. Waves of rain and embedded thunder continues to rotate through the area from southwest to northeast as deep Gulf moisture is advected north into the area ahead of deep low pressure centered over the mid Mississippi Valley. The low will track northeast into the Great lakes overnight and enable a cold front to swing across the forecast area after 06Z. Periodic chances for showers and thunderstorms will continue to impact the terminals until the front passes...with MVFR and possibly IFR restrictions within any of the heavier rain. Southeast winds this evening will veer to south immediately ahead of the frontal passage. Gusts to 25kts will be possible. Low level wind shear will also be a concern this evening. Once the front moves through...should see clouds scatter with even a brief period of clearing as a well pronounced dry slot passes across the region from west to east. Clouds will begin to fill back in through the course of the day Monday however as the cold pool associated with an upper low spreads into the area. Model soundings and RH progs indicate ceilings could slip into the MVFR category by late day although confidence is low at this point. The primary impact to aviators on Monday will be strong wind gusts from the southwest...possibly approaching 35kts at times in the afternoon. Could see a few light showers develop as well later in the day but no restrictions are anticipated. && .HYDROLOGY... Issued at 256 PM EDT Sun Apr 30 2017 As noted above several more rounds of showers and thunderstorms will continue across the area into the overnight. Near record precipitable water values will remain across the area, with sustained moisture transport from the south. The ground is saturated across much of the area, with many creeks/streams and even some rivers already in flood. Thus will continue the Flash Flood Watch for all areas. && .IND WATCHES/WARNINGS/ADVISORIES... Flash Flood Watch through Monday morning for INZ021-028>031- 035>049-051>057-060>065-067>072. && $$ SYNOPSIS...50 NEAR TERM...50 SHORT TERM...50 LONG TERM....MK AVIATION...Ryan HYDROLOGY: 50 is the U.S. government's official web portal to all federal, state and local government web resources and services.