Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 357 AM EDT Tue Sep 18 2018 Valid 12Z Tue Sep 18 2018 - 12Z Thu Sep 20 2018 ...Post-tropical remains of Florence to affect New England today... ...Flash flood threat shifting up to the Middle Mississippi Valley and Upper Midwest... ...Return of monsoonal moisture to enhance thunderstorm chances over southern Arizona/New Mexico... ...Record overnight warmth in place this morning along the Eastern Seaboard... While what was Hurricane Florence has weakened to a post-tropical cyclone, it still maintains a threat for localized heavy rainfall as it shifts into New England today. Additionally, abundant tropical moisture surging up the Eastern Seaboard will maintain a rather mild start to the day. Perhaps up to a couple of dozen daily records may be broken given little ability to nocturnally radiate. Widespread 70s currently blanket the region although some relief will be in sight by mid-week as the extratropical remains of Florence exit into the western Atlantic. During the period, an upper trough will begin to dig across the western U.S. while maintaining quasi-zonal flow over the north-central states. A multitude of disturbances within this regime should provide an impetus for multiple rounds of convection the next couple of days. This is expected to focus just north of a west-east oriented frontal zone which should not move appreciably through Wednesday. Based on the latest forecast, the heaviest rainfall will likely congregate from southeastern South Dakota eastward across southern Minnesota/northern Iowa and into western Wisconsin. A large portion of this area has been particularly wet the past couple of weeks which enhances the threat for future flash flooding concerns. As such, the Weather Prediction Center has highlighted sections of this region in a Slight Risk on Wednesday into the following morning. An area of disturbed weather currently well south of Cabo San Lucas has the potential for tropical cyclone development the next couple of days. Currently the National Hurricane Center has a 40 percent chance for such development as the associated shortwave energy and moisture plume shifts northward in time. Regardless of whether this system develops, its anomalous moisture will be felt across the Four Corners region. As an upper trough sweeps through the southwestern U.S., it will encounter this moist air mass with widespread precipitation breaking out over southern Arizona/New Mexico. While a bulk of the heaviest amounts should shift south of the international border with Mexico, it would not take much to move the focus into the U.S. Given the presence of a quasi-stationary west-east oriented boundary across the center of the country, a fairly potent temperature contrast will be noted in surface observations. On Wednesday, highs across the central U.S. should punch into the low 90s while across the northern tier readings struggle to escape the upper 50s/low 60s. Departures from climatology on either side of the front tend to be in the 10 to 15 degree range. Rubin-Oster For all information on the rainfall associated with Florence and the excessive rainfall outlooks, visit www.wpc.ncep.noaa.gov Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php