I still get the morning paper, even though I'm now paying $4 more for the privilege than I previously thought, which sucks. Anyway. Saw on the weather page that it's supposed to be colder than normal beginning next week. Didn't say how cold, but yesterday Tim Rogers linked to a weathering website proffering models that suggested downright historic highs and lows. So, then. What say you, National Weather Service?
Right now, The Official Word is this and only this:
The upper level pattern over North America in mid January will become oriented in a way that is favorable for a large amount of Canadian and Arctic air to move south and cover the United States. This cold spell is expected arrive on Monday with a strong cold front and last for several days. Temperatures Tuesday January 11th through Friday January 14th across North Texas will be quite cold. Highs are expected to only be in the 30s and lows should range from 15 to 25 degrees. It remains too early to tell whether there will be a chance of precipitation with this cold spell.
But on the other side is the latest chitchat from the National Weather Service, an update full of historical facts and figures that acknowledges the "uncertainty" of forecast models trying to predict the impact of a cold front deep-freezing Dallas while it's presently locked up way up north. Right now, models suggest it won't be as bad as forecasters thought only, oh, a day or so ago. Still, the National Weather Service isn't taking any chances:
The reason why we are watching this so closely is because a 30 percent chance of occurrence is pretty high for an event which would have enormous and widespread economic implications for our region...as we learned in the deep freezes of 83 and 89.
Jump for the full explanation. And do bundle up.
Main weather story is the colder weather expected into the region next week. There remains excellent agreement among the models that a pattern change will occur as blocking upper highs/lows develop and persist across the northern latitudes. A cold air mass will begin to develop and organize across western canada this weekend with surface temps there beginning to fall below 0 as a large sprawling surface high gathers intensity. This canadian air mass is poised to move south and arrive into north texas beginning monday. Since the upper pattern stays blocked...the gates to the north will remain open and cold air will continue to pour south into the central us for several days. Thus it is with high certainty that we can say an extended period of colder than normal weather will occur in north texas next week.
As far as how cold...and whether this event will be one of those memorable decade events...is another question. At least through friday jan 14th...odds are that this cold spell will not be anywhere near record territory and looks comparable to the one last year in early january. Last night i wrote about the benefits of analysis of the source region of these cold air masses... Particularly at the 500mb-700mb level. I dug up the upper air data from a dozen of our biggest cold snaps since 1970. These historic arctic outbreaks unanimously contained 500-700mb temps 5 to 10 deg c colder than what any model is forecasting over canada this weekend. In addition 850mb temps across the northern us are forecast to be about 5 deg c warmer early next week than what our significant outbreaks had. Thus we can make forecast temperature extrapolations based off a model/s upper air forecasts 5 days out rather than relying on a model/s surface temp forecast 10 days out which is obviously prone to more errors.
So for the specifics...monday/s highs should likely be in the 40s as fropa occurs that morning. Lows monday night should be in the 20s area wide with breezy north winds continuing. Highs tuesday through friday look to stay in the 30s area wide despite generally sunny skies. Winds should subside more by mid late week with lows likely in the teens to low 20s each night.
Beyond jan 14th...it is tough to say exactly what will happen. Yesterday/s model runs were more bullish that next week/s cold spell was just the start of something more serious. The latest gfs/ecmwf/gem operational runs and ensemble means at 240 hours are depicting an upper level pattern not exactly favorable for a historic outbreak. They have all trended the blocking high over alaska either too far north or too far west into siberia. This means the positively tilted upper trough axis over the sw us /a crucial component to get an arctic outbreak here...and a key to meeting the requirements of the so-called mcfarland pattern signature/ becomes in question...since a positive tilt trough or kink often naturally develops southeast of an upper high. Without this trough the real arctic air just has a tough time making it this far south. However...about 1/3 of the ensemble members keep this sw trough in tact...and they show a very cold/intense polar low developing over canada and the us in 10 days. Lots of uncertainty and models will continue to change daily. But the reason why we are watching this so closely is because a 30 percent chance of occurrence is pretty high for an event which would have enormous and widespread economic implications for our region...as we learned in the deep freezes of 83 and 89.
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