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Wednesday, 11:59 a.m.
The debate over temperatures this weekend rages on today. The models continue to paint two vastly differing scenarios as to how fast the cooling takes place from the northern Plains and Midwest to the mid-Atlantic states and New England, and how extensive and how strong the cooling will be. Let me just pick off a few charts for you to peruse. The first the European model forecast of 2-meter maximum temperatures for Saturday afternoon:
As stated in Tuesday's post, most places along and south of the I-70 corridor look to be warm with highs of 70 or better. Look further at the models' forecast of 850mb temperatures for Saturday evening:
Now let's look at the very same forecasts off the 0z GFS model:
Clearly the GFS is MUCH colder and MUCH farther south with the cold air than the European model!
For other comparisons' sake, here's the Canadian model:
Much like the European!
Now the latest NAM forecast:
Hmmmm....looks much like the GFS!
Now, if past performance is any indicator of the future forecast, then I would have to come down on the side of the European/Canadian models. The NAM and GFS were insistent during the middle of last week for lots of clouds, cool air and instability showers across central and northern Pennsylvania last Saturday. As it turns out, it was mostly sunny and warmed into the mid-60s! My fear is the NAM and GFS are again leading us down a rabbit trail that will prove to be incorrect, and that the real cooling will take place on Sunday.
Even at that, though, the European model is implying the warm air is reluctant to yield ground from the Ohio River on south, keeping temperatures in the 70s across central and southern sections of Illinois, Indiana and Ohio through Monday, with the warmth hanging on into Tuesday in Ohio! Obviously this is a battle whose outcome has yet to be determined.
Meanwhile, the weather is looking downright ugly for next week. The energy crashing into California Saturday with rain and much cooler air will plow into the Rockies Sunday. Low pressure will reorganize over eastern Colorado and western Kansas by Saturday afternoon, causing rain and higher elevation snows from Montana to the Four Corners area. As the storm translates out onto the Plains Sunday, it will into a road block of sorts, an upper-level ridge who axis will tilt back toward the Dakotas, thus forcing all of the energy underneath it. In turn, an upper-level low will form, all the while an upper-level high will try to form farther north. Even more jet stream energy will come in from the Pacific late this weekend and early next week and feed into the upper-level storm, creating a giant mess that will be in no hurry to cross the rest of the country. That means a threat of severe weather late Sunday and Sunday night from parts of Texas and Oklahoma into Arkansas, and on Monday from the Mississippi Valley into the western Tennessee and lower Ohio valleys.
The risk of flooding will steadily grow from Sunday into the middle of next week as this large storm continues to pull rich moisture from the Gulf of Mexico into its broad circulation. To give you a rough idea of just how wet and how widespread this might be, here's the 0z European model total precipitation forecast from Saturday evening through Wednesday evening:
Even though water temperatures are running below normal in the northern and particularly the northwest Gulf of Mexico, the fronts coming down into the Ohio Valley and mid-Atlantic states this weekend never get close to the South. That means the air mass will have ample time to moisten up over time, and once the upper-level and surface storm start to amble eastward next week, there will be multiple rounds of showers and thunderstorms that, when added up, will probably produce some flooding. As you can see, the model thinks that may happen in two or even three areas - one is across the South, and another from Pennsylvania to Iowa. A third area may be farther west out over the Dakotas and eastern Montana and eastern Wyoming.
Regardless, it is shaping up as a volatile week ahead, and a very wet one at that. And if you're looking for warmth, that will be from I-70 on south this weekend, gradually shrinking into a smaller and smaller area with time during the first half of next week. The upper-level low itself may not fully clear the East Coast until next weekend!
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