Issued: 2pm on Thursday, December 2nd 2021
Technical Forecast Discussion
Short Term (Thursday 12-2-2021 through Saturday 12-4-2021)
Short term period is starting out with what looks like a typical pattern for summer season, just not with typical summer heat of course, with a strong ridge centered over west coast which extends for in all of western half of CONUS into parts of Midwest, Ohio Valley, and most areas of Deep South as of Thursday morning which has lead to milder conditions for much of these areas, including our local region as well. At this same time, we also have a trough dipping into far northern Midwest into Great Lakes and interior Northeast areas which is leading to cooler conditions in these areas. As we progress through the day on Thursday, expect this trough to strengthen a little and dig more southward into all of Northeastern and parts of Mid-Atlantic regions as well while the ridge also pushes slightly eastward as well. Our area in specific is in a interesting situation as we are in the “weakness region” of the trough and the ridge, but upon further inspection, we would see that there is northwesterly flow aloft so there is indeed a very weak troughing overhead. This would also be reflected on surface with a weak cold front expected to move through by Thursday night which cools our area down briefly until late Friday morning. In this same flow, a disturbance is expected dive southeastward into northeastern parts of Ohio where they will likely see a brief period of rain-snow mix as temperatures will be cold enough there, but just clouds expected for our area before they clear out during Friday afternoon hours. This clearing will be courtesy of weak high pressure which moves into our area during this time and we will continue to see dry weather under mostly clear conditions throughout the day of Saturday as well. Going back to upper levels, the upper level ridge will finally be able to flex its way into our area and become more dominate as we move into Friday afternoon through all of Saturday as it will be centered over Central Plains region. Despite the ridge taking control, it is also expected to weaken quite significantly at the same time. On surface level, this would mean that temperatures will not be able to warm up as much as we have seen in Central Plains area. In fact on contrary, our actual temperatures is expected to be slightly cooler for Friday and Saturday compared to past 2 days or so despite the higher heights aloft. Expected high temperatures on Thursday is expected to reach into lower 60’s which cools down into lower 50’s for Friday and Saturday with morning lows lower 30’s during the entire short term period. Temperature anomalies during this period is expected to be 3°F-6°F above normal.
Long Term (Sunday 12-5-2021 through Wednesday 12-8-2021)
Long term period resumes with a weakening ridge centered over us right after midnight hours on Sunday which is quickly pushing eastward into eastward into eastern Ohio Valley and much of Northeast area as of Sunday morning. This ridge by this time is expected to re-strengthen quickly and will expand in coverage as the main axis continues moves off shore Maine by Sunday evening. Our region at this time will be at the far western end of the ridge. Part of the region why this ridge is expected to strengthen has to do with another trough first dropping into Northern Plains and Midwest region which is also expected strengthen as it pushes into Central Plains region by Sunday evening so the downstream ridge also intensifies as result due to overall increased amplification of the pattern. If we look at the 500mb vorticity, you would see strong wind energy in northern branch associated with our trough region and there is another energy in southern branch responsible for brining in the moisture to our region. This southern piece of energy will run out ahead of the northern branch and phase together a little more so widespread precipitation will break out staring Sunday afternoon hours for most of Ohio Valley region, our area included. Sunday will be much milder day as we do have southerly flow at surface levels. Rain intensity will likely remain on the lighter side initially with even better coverage and intensity expected as we move into Sunday night hours with cold front approaching closer to our area. There is some disagreements in modeling in regards to when the rain ends, it looks like Monday afternoon would be the time when rain ends with colder air rushing into our area based on latest forecasts. Looking back at upper level pattern, the trough is expected to strengthen some more by Monday morning period and progress into western parts of Ohio Valley by the this time. This trough will take more of a neutral tilt right at the end of the precipitation event so isolated precipitation could hang around into Monday evening and with cold air coming, there could be changeover to snow showers if any precipitation is still around, otherwise cold air will be quick to fill in and we would have some risk of any remaining wet roads freezing over during overnight hours, but overall risk of that appears low for now. I say lower risk for wet roads freezing over because Monday is expected to become fairly windy day with wind gusts approaching 30mph range so evaporation process maybe quick enough for us to not deal with this issue. Strong winds will also lead to wind chills will be in the 20’s too making it feel blustery outside at that time. Early Indication suggest that we may have total of about 1″ of rainfall by the end of this event Monday evening. The trough associated with this system will finally move into our area sometime Monday afternoon and will quickly make an exit out of our region by Tuesday morning time frame and deliver the cold air sort to speak by this period. For Tuesday itself, surface high pressure appears to be in close proximity so we will have some clouds with cold conditions behind the front. It is from this time period when models diverge in their solutions rather significantly as there maybe another potential storm moving into our area on Wednesday to end the long term period. This potential system appears to be colder one compared to Sunday/Monday system and if everything fall correctly, our area has chance to see first widespread accumulating snow for this season. I want to start out by saying we are still about 6 days out in lead time and there are many moving parts so things will certainly change. Starting with the set up for this system, it is virtually similar to what I talked about Sunday/Monday system in terms of phasing together. All models show in 500mb vorticity field show that there are 2 waves in southern branch systems with first one over southern California and other one by south Texas area and we have a northern branch system Dakotas as Tuesday morning. The 3 key differences in models comes after this period. First thing which needs to be figured out is how strong exactly northern and southern branch is because if north branch is too strong then it would suppress the southern branch and no phasing occurs. Second thing to see is if the southern branch can get out ahead of northern branch like earlier system so it can phase together for a bigger system, even if northern branch dominates, there will be an band of light snow somewhere in the state if this is the case. Third thing to keep an eye out would be on how strong the ridge along Western Atlantic is. There are models like GFS which flexes the ridge for most of Ohio Valley and Northeast region for Wednesday and pushes the surface low further to northwest while ridge is weaker on other models so the storm tracks through favorable area for wintery precipitation in our region. The thing to note is models show different combinations for these 3 key points which is leading to wildly different outputs on model solution. Typical rule I like to follow is wait to see until the time when systems arrives into West Coast area because models typically have troubles dealing with system over North Pacific Ocean and it does not arrive in CONUS until Monday morning so it would be from this time when models should show lot of consistency. Given all the model solutions and factoring in general pattern along with climatology for our area, I will go with mix of rain and snow showers expected for the day on Wednesday with cold air starting to retreat northward. Hopefully I will have more direct answer when I give the next update to this discussion on Sunday. As of now, temperatures on Sunday are expected to be in mid 50’s for daytime highs with same thing for Monday as well, but only thing is it would a midnight high with temperatures falling through the day on Monday with Tuesday and Wednesday high temperatures expected to be in upper 30’s to lower 40’s range. Morning lows for Sunday night will be low 50’s which then drops down into middle 20’s by Monday night and warms back up to lower 30’s Tuesday and Wednesday night. Temperature anomalies during this period is expected to be about 3°-7°F above normal with highest anomalies coming from warm nights during long term period.
