Good morning, and happy Sunday!
Potentially record-high temperatures will work their way into the Pacific Northwest early this week, with the rest of the Northern United States experiencing a bit of a cooldown. In addition to the pattern change, some severe weather is possible for parts of the Great Lakes and the Northeast through Monday.
Current Synoptic Picture
The big feature that is dominating the weather across the CONUS right now is the large upper-level high over the southern half of the United States. In the image above, this is noted by the higher heights over portions of the south, and the broad anticyclonic flow around it. The jet stream is currently located over the northern half of the United States, noted by the tighter gradient of geopotential height lines. Along this jet stream is a weak closed upper-level low in eastern Washington; and lastly, to the north of the jet stream is an elongated upper-level low in central and Eastern Canada.
According to the GFS analysis, most of the United States is experiencing anomalously high 500mb geopotential heights, with exception to the northern Great Plains and the western Great Lakes Region due to the double barrel low in eastern Canada.
Western United States
As a result of the passing weak upper-level that we talked about earlier, yesterday brought mostly average temperatures to the region, Starting today, however, a 500mb ridge will continue to build over the West Coast, bringing much-above average temperatures across the region – particularly for the Pacific Northwest.
According to the GFS 5-day temperature outlook, the Pacific Northwest should see temperatures more than 10 degrees F above average! This translates to temperatures well into the 90s for locations like Seattle and Portland – hot enough that daily temperature records may even be broken in and around Seattle on Tuesday.
As far as any precipitation goes, most of the West Coast will remain dry for the next few days, with the only places receiving rain being the Desert Southwest and locations east of the Rockies – as a result of Monsoon-season thunderstorms and the interactions with the weakening upper-level low with energy east of the continental divide, respectively.
Northern Great Plains and the Northeast
In the Central US, the main story is the upper-level low to the north that will be affecting the northern Great Plains. By this afternoon, anomalously low 500mb geopotential heights will continue to be present in the northern Great Plains, with positive anomalies in the southern half of the country.
As expected, these negative height anomalies will translate to some below average temperatures at the surface, which is shown by the 1-day temperature anomalies per the GFS
By mid-week, the energy from the weak upper-level low currently in eastern Washington will mix with another troughing feature currently in western Canada bringing a second pulse of lower geopotential heights and correlating cooler surface temperatures. At the same time, the upper-level low over Ontario will move eastward, cooling things down in the Northeast.
The five-day temperature anomalies show below-average temperatures for much of the northern Great Plains and parts of the Northeast due the passage of these upper-level systems and anomalously lower geopotential heights.
Of course, with the passage of these systems, the atmosphere is forcing already-in-place warm air out of the way with cooler air – leading to the development of some thunderstorms and bringing the threat for severe weather to the region.
Currently, the National Weather Service’s Storm Prediction Center is highlighting the eastern Great Lakes region for a slight chance for severe weather today, and parts of southern New England and the Mid-Atlantic for severe weather on Monday.
Southern Plains and the Southeast
East of the Rockies, the northern half of the country gets to cool off a bit, for the southern half of the country, unfortunately that’s not really the case…
While the upper-level ridge does weaken some, 500mb heights are still anomalously high across much of the region, bringing with it more above-average temperatures – which we saw in an image in the section above.
The worst of the heat will be for parts of Texas and Oklahoma, where the sinking air near the center of the upper-level high pressure will significantly decrease the chance for afternoon showers or thunderstorms that will help to cool temperatures down. This lack of chances for rain becomes apparent when we look at a precipitation map through next week, where the only place in east of the Rockies that misses out on rain is most of Texas and Oklahoma…
Elsewhere across the Southeast, the typical threat for afternoon showers and thunderstorms will continue to provide ample chances for rain each afternoon.
