Lots to discuss with the week ahead. So I will break it down into parts...as it will be one heck of a weather story this week to tell.
PART I The Warm Front
Impact timing: Later tonight/early Monday
The front is spreading a band a rain in advance of it now across IL. It is running up against the cold air in place and lending hand to a freezing rain event in that area.
Thankfully, for us, we will see enough warming to help get us above 32 by midday. I think it will be close for areas to the north/northwest of Louisville---so I will monitor that the next few hours. The good news---this is a warming event---so any icing threat will be short-lived as we warm well into the 40s later today. I went on the higher end of model guidance to near 50. We usually warm up well with warm fronts. We won't drop much tonight as a south wind takes over. That will lead to a mild Monday with highs in the mid to perhaps upper 50s. Any rain activity looks spotty and relatively light. Many areas likely will stay dry on Monday the way it is looking now.
PART II Near Record Warmth
Impact timing: Tuesday afternoon
We will move firmly into the warm sector of the storm system on Tuesday. How much the clouds thin will determine our high that day. With cloudy skies....mid 60s are likely.
Any sunshine will push us closer to 70. The record high for Louisville that day is 73. Right now, that looks safe to me.
PART III Severe Storm Threat
Impact timing: after 11:00 Tuesday night- 5:00 Wednesday morning
The models are in pretty good agreement that a wave of heavy rain/storms will pass through the region. But there are some setup differences that will impact areas of greatest concern.
First off----the main pieces of energy are displaced when looking at GFS vs NAM. GFS has the vort max riding along the cold front and digging through the Ohio Valley across TN.
Tornado threat would be found just ahead of that with a strong risk for damaging winds to the north of that across our region.
The NAM has the vort much more to the south. Tornado threat would be pretty high across MS/AL with the NAM. We would have a high wind threat---but not as intense as if the vort were closer. Interestingly enough, the NAM idea would likely lead to an area of low pressure that would track across eastern TN---and could even enhance a closed low snow threat on the NW side of that low across KY/TN before precip ends.
Instability is hard to come by for late January---especially during a nocturnal event. That isn't unusual. But the thing to keep in mind as you only need a small amount to create a severe weather event.
Latest GFS instability for Tuesday-day is pretty decent to our west.
By late Tuesday night---it drops off quite a bit to about 150-200. Not impressive---but there is a chance the models are too low with these values at this early stage.
But here is the concern---the winds aloft. Quite impressive indeed! The wind fields aloft would exceed 90 kts just above our heads when the storms pass through.
That could easily give the line of storms a wind gust potential of at least 70 mph! But before we take that info too far----we do have a saving grace in our area with these events. Sometimes we see an inversion that never allows the winds to drop all the way to the surface. In the past 2 years---I have seen that be the case about 70% of the time. However---it is that other 30% that concerns meteorologists in these setups. If we start hearing of high wind gusts and/or wind damage to our west as the line approaches---it is safe to say that there is no block for those winds and red flags should be raised.
Latest SPC outlook for Tuesday is just to our west---- in theory--that threat will head east overnight.
This is just one of those setups that we won't really have a good handle on until Tuesday to get weather balloons in the air that day to sample how things are lining up. So right now we are just talking *potential* and trying to give a heads up to stay tuned for updates---whether good or bad ---with this threat.
PART IV The Rain Ending as Snow
Impact timing: Wednesday night
This goes into the discussion I pointed out above about whether or not we have a closed low nearby or just a cold front. If just a front---a typical rain ending as light snow and shutting off would be likely. Little to any accumulation with that. If a closed low does pass to our SE---we may see a more organized backlashing of snow with a better chance at accumulation. I have seen support for both ideas on various models. So right now--we are just stating rain ending as snow as specifics are too challenging at this early stage.
PART V Clipper # 1
Impact timing: Late Thursday night/early Friday
This would really be our first true clipper of the season. It will dive across MO..then head due east toward VA by early Friday.
We will have a very cold air mass in place---so snow ratios look to be very close to 20:1 right now. This mean .10" of liquid could produce a couple inches of snow. GFS/EURO vary on the track a bit with this ...and how much moisture.
But I think for some in our area---this would be the first accumulation of the season---and perhaps the heaviest thus far. Clippers are interesting around here. Usually fully of surprises and can "overachieve". Something to watch as we get closer.
PART VI Clipper # 2
Impact timing: Saturday night
Right now, this one looks to not dig as far as # 1-----so we plan to keep the track to our north. I had small snow chance this morning for Saturday---but that could be removed if the northern track holds.
PART VII Chinook Winds
The longer term is interesting. There appears to be a trough that will get stuck over the eastern USA. We would be on the edge of this.
On the western side...there is a huge ridge all the way up into Canada. This leads to easterly winds down the Rockies---called the Chinook Winds. These are compressing winds that downslope off the mountains into the Plains. These can be "snow eaters" if there is a snow pack.
I am still trying to figure out how far east the impact of the Chinook Winds will be for us---as the trough over the east may keep a firm gripe on our area. Just a tough call this early.
AO is showing signs of dropping again---so the Polar Vortex continues to be on the move.
And the PNA remains slightly positive---which means any cold that develops...can be long lasting.
Interestingly enough---I checked the latest on El Nino/La Nina---and we have been in a weak La Nina as of late.
Okay..hand is hurting from typing. That is all for now :)