WINTER STORM INCOMING....
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A BIG WET STORM ON THE WAY...
Our weather has been more than friendly the past few days but time is quickly running out as a mid-winter storm takes aim on the Midwest. Before I get to that, you can see the snow cover that existed has largely been depleated with the warmth our newfound warmth. This high resolution satellite taken with fair skies Tuesday afternoon reveals the snow pack north of a line that extends from Ames to just SE of Dubuque into extreme NW Illinois.
We have one more decent day to enjoy with rain and snow holding off through the day Wednesday. Highs will remain well above normal in the range of 40 north to 45 south. Clouds will increase from north to south as the day progresses and moisture increases ahead of the storm.
DYNAMIC SYSTEM WITH HEAVY RAIN AND SNOW...
Attention then shifts to the storm system and deepening trough that spins up a well organized surface low that tracks on a line from SW Missouri to just NW of Chicago. Initially, cold air is lacking and precipitation begins ar rain Wednesday night. However, NW of the surface low dynamic cooling for the strengthening low will change rain over to snow in the NW half of my area, especially near and NW of a line from Mt. Pleasant to the Quad Cities and on to Freeport. Currently the wet snow should be heaviest in my area near and NW of a line extending from Iowa City to Anamosa to about Galena. For now, The NWS has posted a Winter Storm Watch for that parts of that area Wednesday night and Thursday. I expect the NWS will either push these further SE into more of eastern Iowa and NW Illinois. They may even go winter storm warning in counties that are in that line from Cedar Rapids to Dubuque.
As you can see, the current official forecast from the NWS has the heavier amounts further west. That may not be the case and I will explain when I get to the snowfall outlooks of the models below.
Here's another perspective further east.
Now the question becomes where the precise storm track ends up and when the transition from rain to snow takes place? As you can see below the energy Tuesday night was still over the Texas panhandle.
As it lifts NE the heavy snow band forms just NW of the surface low. If the track is altered just a bit (which is still possible at this distance), that could shift it west or east. Additionally, if the rain changes to snow earlier, amounts would be heavier. Conversely, if the transition takes longer amounts will be less. One thing is for sure the system has ample moisture. Water vapor is projected to exceed 1.25 inches in spots on the EURO.
Incredibly, that is over 450 percent of normal levels! That is 6 standard deviations above the norm. Wow!
That ensures an anomalously heavy precipitation event with departures over the next 5 days as great as an inch or more in may eastern Iowa locations.
Here's what models are indicating for liquid equivelent totals from the storm.
The EURO
The GFS
The 3k NAM
The Canadian hi-res run
Total precipitation by type on the EURO
Total precipitation by type GFS
The latest models are coming in now and here is what they are suggesting for snow totals. Keep in mind, these are not forecasts, just raw model output which we utilize to make snowfall forecasts. As you can see they all have slight differences. The hope is that there is good general agreement which increases confidence. (The content of fresh model runs are always monitored as they can indicate trends in track or moisture that might alter amounts). Another consideration regarding this snow is that where it occurs, it will be very wet and heavy to push. Take a look at the new runs and l will comment below.
The EURO
The GFS
The 3k NAM
The 12K NAM
The HRRR
THe Canadian hi-res HRDPS
The big take-away for me is that models have shown a distinct tendancy to track the storm 50-70 miles further southeast. They are also somewhat stronger on the intensity. If this trend holds (we will know more in the morning runs Wednesday), heavier snow as I mentioned earlier, could reach closer to the Mississippi and points north and west. The potential is there for 4- 6 inches of heavy wet snow. I could also see banding creating a narrow swath of 8 inch amounts from near Iowa City to Anamosa on to Dubuque. It also appears during the peak of the storm winds Thursday could gust to over 30 mph+ from the NE. Due to the heavy wet nature of the snow it should not drift much but low visibilities could develop in areas of heavy snow.
There are still a lot of moving parts to this storm with the biggest challenge being the timing of the changeover from rain to snow and the resulting impact on snow totals where it happens. As it stands now, the area from about the Quad cities north and west will see the worst of the wintry impacts....if the track holds! Further southeast lots of rain before a late changover to snow with some light accumulations looking more likey, say 1-2 inches. I will have an update at some point in the afternoon Wednesday. I have a doctors appointment for a minor procedure or would have it for you sooner.
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