Posted at 5:15 PM on April 26, 2012
by Paul Huttner
Frost & freeze advisories north & east of the metro Friday morning
Growing snow chances close to the metro overnight Friday into Saturday AM?
"Temperature critical" - models right on the freezing line for rain/snow early Saturday
Cool weekend highs in the 50s at best
64/43 average high/low for the Twin Cities this weekend
Warming trend next week - a return to 70s?
Frosty start Friday:
Right on schedule. This weekend is on average the date of the last frost of season at MSP Airport. Cool Canadian high pressure is nosing into just in time to keep us "close to average" with another shot of frost close to home this weekend.
After our record warm March, it's easy to wave our hands and scream "extreme weather, extreme weather" with frost this time of year...but it's absolutely as normal as normal gets to see frost in late April in these parts.
So, what about snow?
Sometimes in Minnesota it seems we need to be reminded where we live. It snow here in April, sometimes even in late April. MSP Airport average about 3.1" of snow in a "typical" April. So far this April? Just a trace at MSP, closer ot a foot in some places up north.
There are still big model differences on our chances for snow near the metro overnight Friday night into Saturday morning. Here's the best breakdown of the system at this time.
Low pressure tracking from near Kansas City Friday night through northern Missouri into Illinois by Saturday. The NAM suggests closer track to MN. The GFS and European models seem to suggest a track farther south.
The system will draw up some moisture from the Gulf of Mexico and inject it into southern Minnesota. Drier air at the surface will eat away at the northern edge of the system in Minnesota. One of the big questions with this system remains how far north will moisture be able to ride as it bucks the dry intrusion from the north? This result will be a rapid cutoff in rain/snow and the cloud shield on the systems northern edge.
This is the biggest question with this system.
Models agree the system will be warm enough for all rain Friday and Friday evening. Sometime around midnight, forecast models strongly suggest that enough cold air will work into the system that a changeover to all snow will occur on the systems northern edge...probably over southern Minnesota.
The NAM model is the most aggressive with this changeover, and with pushing moisture north toward the Twin Cities. It suggests a few inches of wet slushy snow are possible by Saturday morning. It could be on to something, or it could be "model terrorisim." Sometimes the NAM gets a little hyped about potential snowfall.
Check out the (gulp) graphic below.
The GFS is less impressed, and suggest maybe a few wet snowflakes mixed with rain...and most of the heavier precip remains south of the metro.
Bottom line? At this point there is a chance of rain mixing with or changing to snow Friday night into Saturday morning. Let's see if the models can come up with a more consistent solution by Friday evening.
Any way you slice it, this weekend is going to feel a lot colder than our flirtation with 70s earlier this week. Morning will trend frosty in clear areas, and Saturday may have trouble climbing out of the 40s.
Sunday still looks to be the slightly nicer day this weekend with some clouds and sunny peeks...but temps will remain cool with highs in the 50s.
Warmer next week?
Overall the pattern appears to shift for the warmer, and wetter next week.
Slow moving low pressure may set up in Nebraska and pump warmer air..and more moisture into Minnesota. We could see a few bouts of showers and T-Storms next week. We need the rain, and if that GFS suggested pattern holds, some places in Minnesota could get heavy soaking rains next week.
As long as it's at night, during the week right? If only I had the power to "schedule" our weather to make people happy. Wait, I'm not sure I'd want that job either!