Prepare for possible triple digit temperatures from May 19-23 throughout the New York City metro area when The Big Apple will be roasting.
An amplified upper level pattern will be in place for the beginning of next week, with an anomalous ridge over the east- central U.S. supporting an early season heat wave, and a strong trough over the Rockies that will bring a round of late season snow for the higher elevations of Colorado and Wyoming. At the interface of these two features will be broad diffluent flow over a strong cold front that will cross the Plains and Midwest, bringing multiple rounds of heavy rainfall and strong/severe thunderstorms. ...Guidance/Predictability Assessment...
Most of the latest deterministic and ensemble guidance remains well-clustered through a majority of the period, with the overall pattern featuring a shifting trend from more amplified flow to quasi-zonal. An initial upper-level shortwave within mean central to western U.S. troughing and accompanying low pressure/frontal system reflection at the surface over the Great Lakes shows typical smaller-scale differences in progression and track at this time frame but follows a mostly agreeable trajectory northeastward into Canada. A trailing cold front will spread towards the East and Gulf Coasts with subtle differences in frontal position and a potential southern stream short-wave bringing uncertainty to QPF coverage/amounts particularly over the south-central U.S., but again with an agreeable overall pattern. The progression of the upper-wave/surface low pressure notably slowed in the CMC compared to the other guidance by the middle part of the period, with the low stalling and weakening in the vicinity of the Northeast compared to lifting northeastward into Canada. As the flow trends more quasi-zonal, uncertainty increases with individual northern stream short-wave timing/progression across southern Canada and into the northwestern to north-central U.S. with growing divergence overall between the deterministic guidance with regards to at least one if not more possible systems. The updated WPC forecast was based on a composite blend of the 06Z GFS/EC AIFS and 00Z ECMWF/CMC/UKMET for the first part of the period given good agreement, with the CMC dropped by mid-period given the outlier nature of the northeastern upper-wave/surface low progression. A contribution from the ECens and then GEFS means replaced the CMC and then time-limited UKMET which also helped to trend towards a compromise solution over the northwest to north- central U.S. given growing uncertainty and allowed for good WPC forecast continuity. ...Weather/Hazards Highlights... A dynamic storm system crossing the Plains will bring widespread showers and thunderstorms from Texas to the Ohio Valley ahead of a strong cold front.
On Tuesday, the best focus for heavy rainfall is expected to be across Texas and extending eastward to Arkansas and the Mid-South as the front intercepts deeper moisture and slows down in its forward progress. A Slight Risk of excessive rainfall remains outlooked across portions of south-central to eastern Oklahoma/the Red River Valley and into northwestern Arkansas. Spread amongst the guidance with regards to the frontal position as well as potential influence of a subtle southern stream wave has resulted in greater uncertainty with regards to the highest QPF location/coverage across the southern Plains into the Ozarks and southward towards the Gulf Coast. Therefore, some adjustment of this risk area may be necessary in the coming days, though plentiful moisture/thunderstorm potential does at least support the potential for scattered flash flooding. Additional heavy rainfall is likely going into Day 5/Wednesday with a broad Marginal Risk extending from western Texas to the central Appalachians. In the temperature department, heat will be making headlines for much of the Eastern U.S. through the middle of the week, with the hottest conditions across interior portions of the Mid-Atlantic into the Carolinas where highs are likely to reach the lower to middle 90s. This will likely be warm enough to establish some daily record highs before a cold front brings relief from the Ohio Valley to the Mid-Atlantic/Northeast by Thursday with much cooler temperatures forecast heading into Memorial Day weekend. The opposite will hold true for the Intermountain West and Rockies with below normal readings to start the week, and snow for the higher elevations, followed by a moderation trend.