Monday, 11:55 a.m.
One of the things I do each morning is sit down and analyze a weather map of the U.S. and Canada. I'll start by contouring the isobars, then I'll place the appropriate highs and lows on the map, then add in fronts of any kind. I'll then look at the radar composites and hatch in the areas of precipitation, then scallop in the areas of cloudiness. It gives me a nice snapshot all rolled into one of the weather from north to south and east to west.
As I analyzed this morning's weather map, it was pretty easy - a strong low pressure area over Nevada, a couple of waves of low pressure over southeastern Colorado and Iowa and a nice high pressure area over North Carolina. To the north, a giant high over Saskatchewan to the tune of 1041mb. Underneath that high is a lot of cold air that is drilling across the Northwest and northern Rockies into the northern Plains. That's resulting in some snow in parts of Montana and Wyoming.
The arctic air is going to be split into two pieces, though. I've already mentioned the part moving into the northern Rockies and Northwest. The rest of it will head eastward with the large surface high. Look at the projected temperature anomalies for tomorrow from the 6z Oct. 28 GFS ensembles:
You would think with such a strong high on the weather map and a storm likely to reorganize over the western Plains and eastern Rockies that a lot of cold air is going to sweep across the Plains then into the East. Such will not be the case this week. A big part of that is tied to the splitting of the cold air into separate entities, rather than keeping it consolidated. The large surface high will head to upstate New York and New England late tomorrow and tomorrow night, pushing a chunk of the arctic air ahead it. Already by Wednesday, though, a weak disturbance will scoot across the Plains and bring warmer air to bear across the Mississippi Valley. Look at the upper-level setup tomorrow morning:
Compare that to Wednesday evening:
As the upper-level low over the West begins to open up and migrate eastward, the heights downstream will rise over the eastern third of the country, so what chill moves into these areas tonight and tomorrow is already being attacked Wednesday. Notice also that the upper-level ridge over the eastern Gulf of Mexico will set the stage for the low coming out of the central Plains to head northeastward toward the Midwest and the northern Great Lakes. In turn, southwest winds will bring warmer air right out of the southern Plains into the Ohio Valley and Great Lakes later Wednesday into Thursday and into the East Wednesday night and Thursday.
Behind the storm and its attendant cold front, the air mass that remains to cross the Plains and Mississippi Valley won't be anywhere near as cold as it is right now from Montana northward. Cooler, yes. However, the departures from normal will be smaller Friday in the Ohio Valley and Saturday and Sunday in the East than they will be in the northern Rockies and Northwest today and tomorrow.
So, despite the very strong surface high moving into position today, it won't deliver the kind of big chill that you would normally expect!
One strong cold front moving through the Great Lakes and Ohio Valley this afternoon will be followed by another one to begin next week, and the recurving of a Typhoon in the western Pacific may enhance the cooling behind it.
A quick surge of heat and humidity is heading eastward today from the central and southern Plains. Behind it will come still another refreshing air mass later this week, while the West stays largely hot and dry.
Tropical Storm Arthur has formed in the Atlantic east of Florida and will likely graze eastern North Carolina Thursday night and early Friday before passing south and east of New England late Friday and Friday night.
An area of low pressure east of Florida is likely to develop in the next three days, and could become the first named storm of the year in time. It will delay the passage of a cold front off the East Coast until week's end, keeping the East very humid until Friday.
Wet weather has plagued the Midwest and northern Plains this month, and it's helping to keep temperatures down across much of the country from the northern Rockies to the mid-Atlantic states and New England. Look for this to persist into next week.
High humidity is in place across a large part of the country now, and it will remain that way through the weekend, helping to fuel showers and thunderstorms that can contain flooding downpours in some areas.