PINEAPPLE EXPRESS TO BRING MORE SNOW THIS WEEKEND...
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THE PINEAPPLE EXPRESS IS ROLLING
HEAVY WET SNOW:
A concentrated band of moisture extending from the tropics to the mid-latitudes known as the "pineapple express" is spinning up another storm that will find its way to the Midwest Saturday. From all indications, the potential is increasing for another healthy snow event over the northern half of my area. Of course, the usual pitfalls such as the track, amounts, intensity, and the rain/snow line must be ironed out but the picture has become clearer.
For the most part, models have remained consistent in their solutions with one exception, the GFS. It is a notable outlier depicting thermal profiles which contaminates its snowfall forecast. I have basically thrown it out and will be leaning heavily on the EURO and 12K NAM and their handling of the storms evolution. I think the existing deep snow cover will lead to the colder and further southward placement of the snow band that the EURO and 12K depict.
Every storm is reliant on energy and moisture to make its mark. The animation is cool in that it show the concentrated energy come out of the SW in the form of a closed upper air low at 500mb. That's the forcing that provides the lift necessary to generate precipitation.
You can see how it changes the game with regards to available moisture. The PWAT values Thursday morning were under 2/10ths of an inch.
Towards Saturday evening they have increased 5 times in southeast Iowa where amounts over an inch are indicated. That's a well endowed storm by January moisture standards.
That shows up well with PWAT anomalies more than 3 times what's normal Saturday.
This animation shows how the storm explodes once it encounters the required moisture Saturday morning in Kansas. The precipitation shield blossoms and quickly advances northeast ahead of the upper air energy. Fascinating to see.
Here you can watch how the EURO paints the snow band as it evolves Saturday afternoon and continues into Sunday morning.
The one issue that makes this storm a challenge to forecast as I mentioned above is the thermal profiles. 850 temperatures of 0 or colder is the magic threshold known as the rain/snow line. Near the onset of precipitation the EURO has this key parameter laid out near I-80 in Iowa before it gradually veers southeast near the Quad Cities. That indicates rain or a mix of rain and snow south of I-80 until thickness values collapse as the storm center moves east. That will limit the accumulations in my southern counties, especially near and south of HWY 34. That issue will be in play as far north as I-80, just not as pronounced. This is the one concern I have about snow totals with this system and we should have more confidence on how that plays out later Friday
Before I get to the snow totals on models, here's the Vegas (make that EURO) odds on amounts as of Thursday night.
1 inch or more.
3" or more
6" or more
With that, here's the model snowfall forecasts. This is the raw output with no human intervention. These are not forecasts, just the various depictions that are on the table for forecasters to look at and make their predictions from. Based on what I have seen, I would think the potential is high for a winter storm watch for the area near and especially north of I-80 at some point Friday. That is in the hands of the NWS. ***UPDATE*** Ironically, I was just alerted by the NWS in the Quad Cities that a winter storm watch has been issued for that exact part of my region. I commend lead forecaster Andy Ervin on his placement and willingness to get the watch out in a timely manor. These are the counties involved.
And now, the latest snowfall forecasts from the various models.
The 3K NAM
The 12K NAM
The Canadian GEM
The GFS ensemble
Since we are still 36 hours away from the event there are no doubt tweaks to be made but the shovels will again be required by Sunday morning. The back-breaking work appears to be in the northern half of my area. Of course, where I am in Portland, Maine all I can do is watch with envy. Since the big 18" storm of December 17th, nothing but a few dustings here. The grass is always greener on the other side. I'll be back in the Quad Cities for tornado season. That means nothing will happen so good news for you back in the homeland! Have a stellar weekend and roll weather...TS