While we bask in some unseasonable warmth, most of us are aware now of the big changes that lie ahead for the weekend. Saturday is the official start to winter, and that is when things really go downhill for parts of the area – and it's not just for wintry weather.
The storm system at hand is coming into our region in two parts. First, the Arctic cold front is the leading edge of that cold air mass that will envelop the area by Friday morning. There won't be a lot of moisture with this feature, but temperatures may drop to near freezing that day, which means any showers or drizzle that occurs could freeze on contact. The main threat of that would be north and west of Tulsa.
The second part of the system is a powerful upper level low that drops along the west coast over the next day before making a bee-line towards Oklahoma this weekend. That is the feature that will draw up a big fetch of moisture. It's almost a guarantee now that it'll be precipitating this weekend. The question is how cold the air may be. Just 10 degrees difference in air temperature may separate an ice storm from plain rain and even severe weather.
The latest data supported by all of our main computer models show a warmer trend for Saturday, when the bulk of the precipitation arrives. There may be enough cold air at the surface remaining, from the I-44 corridor to the northwest for a window of freezing rain early Saturday morning. However, winds may veer to the south and bring up warmer air during the day, cutting off the icing potential. Fortunately, this is not a classic ice storm set-up. With a low at 32° early Saturday in Tulsa, there's not much opportunity there for icing to occur unless something changes. The first attached map shows the areas at risk for at least some freezing rain. Tulsa can expect mostly a cold, plain rain during the day.
The other side of the storm system is the threat for severe weather. The Storm Prediction Center is already highlighting an area from northern Texas to the Mississippi Valley for an outbreak of severe thunderstorms, including the risk for tornadoes. This clips our southeastern-most counties. (See second map) While it may be too cool here for any significant severe weather (and too warm for ice) on Saturday, we still could have some heavy thunderstorms with a flooding potential. See the third attached map for how much water may fall between now and Monday.
The final phase of the system will be the wrap-around precipitation as the main upper low passes directly over us. Colder air aloft will allow for a transition to snow from west to east Saturday night into Sunday morning. The heavier band of snow is likely to set up to our north in Kansas and Missouri, but we could still have some accumulating snowfall from Tulsa to the north. Our final map shows that potential. The biggest winter weather travel impacts will be in north-central and northwestern Oklahoma.
The system clears the region Sunday afternoon and we're left with cold, dry air. As of now, our thought is that we'll miss out on the heavy snow totals. This is great news to local travelers, but bad news if you're hoping for a White Christmas. Unless this system takes a more southerly track (which isn't too likely), we'll be left with a mostly brown Christmas, especially as temperatures gradually rise next week.
In any case, it's a HUGE weekend for holiday events and travel, and the take-away is to plan ahead. We may just have to contend with wet roadways on Saturday and maybe a few slushy roads on Sunday. However, it's a powerful system and nothing is set in stone. Tulsa lies awfully close to a more significant winter weather event and the threat for severe storms and flooding so it's worth watching closely. The next few days will be the best time to take care of that last-minute Christmas shopping from a weather standpoint.