A PRICE TO PAY FOR A WARM DAY...
Temperatures will be on the way up Saturday as a late winter storm spins up to our west. We'll be situated in the warm sector allowing spring-like air to take up residence for one last day. Just how warm depends on the amount of sunshine that can filter through what should be a mostly cloudy day. If we can manage an hour or two of broken sunshine the potential is there for highs to reach into the lower 70s, but mainly in the southern half of my area. The far north could be 10-15 degrees colder. Some spots in the south could push records for the date which look like this March 5th.
The Quad Cities (Moline) 69, 2009
Cedar Rapids 72, 1921
Dubuque 69, 1921
Burlington 73, 1910
Even with limited sunshine, the hi-res HRRR shows 3:00pm readings that in most areas would be the warmest of 2022 so far. Here's hoping!
The next order of business is showers and thunderstorms and any severe weather potential. If there is one critical ingredient to any severe weather threat it's moisture...the more the better. In Saturday's situation a narrow plume of rich moisture (by March 5th standards) is drawn into eastern Iowa towards evening when dew points on the HRRR are shown reaching the upper 50s to 60 in Iowa City and Washington.
Those dew points are on the low end of the severe weather threshold but enough with highs near 70 to create CAPE (instability) of up to 1,000 j/kg.
Again, CAPE of 1,000 j/kg is nothing special but if forcing and shear can reach sufficient levels it's enough for strong to severe thunderstorms. In Saturday's set-up the shear is significant and the dry slot formidable but the timing after sunset is not. As it looks now storm initialization takes place at peak heating in central Iowa. It also looks to be surface based which means some rotating supercells are possible out that way. While some discrete cells are possible around initiation, it appears those updrafts would go linear quickly and evolve into a broken squall line. That charges east towards my area towards early evening. However, the better dynamics move more northeast than east and with sunset storms should weaken as the updrafts are tougher to sustain. Below is a simulated radar on the HRRR depicting a broken squall line entering eastern Iowa around 4:00pm
With a 50 kt jet overhead storms may tap that wind energy and bring it to the surface and there may be some gusty winds up to 60 mph, even in areas where there is minimal convection ahead of the advancing dry line. In the stronger updrafts some brief downpours are likely but the fast forward movement should keep amounts low. Most amounts may end up 1/4 inch or less. The exception to that would be in the NW third of my area where storms should be at their strongest in the earlier stages of convective development. As I mentioned yesterday, the timing and evolution of the set-up is reminiscent of the December 15th derecho which produced numerous tornadoes and high wind reports in western and central Iowa. The critical difference is the strength of this system is substantially less which assures a far less robust outcome.
For my area the bottom line is that a few strong storms with gusty winds and perhaps some small hail will be a possibility Saturday evening in my far western counties, especially west of a line from Independence to Cedar Rapids, and Iowa City. The further east you go the lesser the risk. The tornado threat should be more of a concern in central Iowa. As always, severe weather is fluid and until we can see all the players on the field later Saturday it's a situation worth keeping an eye on. I would not be surprised to see a tornado or severe thunderstorm watch issued for some of my far western counties. SPC currently has the majority of my area in a slight risk outlook for severe weather.
By midnight, the dry slot has pushed through the entire area and quickly shuts down precipitation from west to east as it advances into the Great Lakes. Winds will increase behind the cold front and by Sunday morning temperatures are down in the range of 30-35. Sunday looks dry but noticeably colder with highs generally in the low to mid 40s.
The next system is hot on its heels and arrives from the SW late Sunday night and Monday. This time around temperatures are expected to be just cold enough aloft for snow to develop. There's still some uncertainty about the track and overall impacts of the system but clustering is coming in line with a swath of snow that overspreads most of my area Monday. Surface temperatures will be marginal so this will be a wet sloppy event. Fortunately, amounts should be light in the general range of 1-3", maybe 4" in a couple spots. The focus of the heavier snow continues to wobble around a bit but a consistent signal is there that the main band goes right through the heart of my area from southwest to northeast centered on or just west of the Quad Cities. Here's what the latest models are indicating for snowfall totals. This is just raw data, none of these are official forecasts. This is the guidance we use to develop trends and eventually forecasts.
The 12K NAM
We should have a good handle on trends later Saturday as we get within 48 hours of the event.
On a related note, another storm is expected to rotate out of the mean trough out west late next week. Track will be critical to precipitation type but rain, snow, or a mixture of both looks likely. Through it all and well into next week temperatures are expected to be below normal. The EURO shows these temperature departures for the 10 day period March 9th-19th.
With that less than thrilling ending, it's time for me to call it a post. Have a sensational weekend and pray for peace! Roll weather...TS
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