Adkjsfkdjs... Freeze possible....

Strong southerly flow ahead of an approaching storm system pushed the temperature up to 80 at DCA (Reagan nat'l airport) today. Despite our late spring like weather for the past week, we are still at risk for frosts and freezes. The average last freeze for the area is April 15th. Planting of tender plants is not recommended most years until late April. we have been in for quite a roller coaster ride for the past few years. Spring 2012 featured the warmest spring on record, with the growing season starting in late march. 2013 had a prolonged cool period, and this year it seems like we flipped the switch from March to April. We went from 34 and snow on March 31st to 65 and sunny the day after and we have gradually warmed ever since. The cherry blossoms have bloomed, trees have budded, the pollen count has spiked, and even the grass needs to be mowed but that being said, winter just refuses to die. Pretty sure I've said that more than once.

Now once again, spring will display its bipolar tendency and swing another cold front our way. Tomorrow, our high will be in the morning and temperatures will drop throughout the day as cold air rushes in from the west following a cold front passage. Sounds familiar, right?  Showers and possibly thunderstorms will accompany this front as temperatures drop into the 50s during the day and down near 30 by Wednesday morning. That 30 degree temperature forecast is concerning because the growing season has begun. Steps need to be taken to protect tender plants from the freeze. The NWS has issued a freeze watch, meaning that there is a decent possibility of a damaging freeze.

In addition to the freeze, models show the possibility of a little bit of backside rain/snow/ice mix of the non accumulating type as cold air rushes in, meeting with lingering moisture. However, models do vary on the amount and precip-type. Some show weak waves of low pressure riding up the front, which would focus more life and moisture, producing more precip while others show a straight frontal passage, with no low pressure waves.  Here is a quick rundown of the models:

EURO:

The Euro is warm and wet, with no snow for us. Temperatures stay in the mid to upper 30s as the cold air struggles to get over the mountains.

















GFS:

The GFS is the coldest and snowiest of the models, simulating .1-.2 inches of liquid equivalent frozen precip for the area. That would translate to at most, an inch of snow on elevated surfaces if taken verbatim. The temperatures depicted are record lows for those dates. Compare the temperatures with the Euro, which has a higher grid resolution. The Euro is 5-10 degrees warmer. Taking the warm ground temps and some logic, you can assume that the GFS is too cold. Downsloping would either wring out the all the moisture against the mountains, giving us dry cold  or it could warm the air through compression or it could do both. In a way, areas farther east have a better chance of getting snow because they have a better shot at getting residual moisture after the front passes.





NAM:

The NAM keeps snow well to the north and west of us. It basically highlights the issues discussed above about the GFS, drying us out fast, and keeping us warm.

















CMC:

The CMC strikes a balance between the GFS and the NAM, keeping the snow right along the fall line where elevation would help with the cooling. It is much more believable than the GFS.

















SREF:

The Short Range Ensemble Members model gives us a mean of .23 inches of snow. However, out of the 22 members of this model suite, only 7 members give us any snow. The mean is .23 inches but chances are we will get nothing.

In any case, any accumulation is very unlikely if not impossible. There may not even be any frozen precip because the models tend to bring cold air over the mountains too quickly when compared to observations. Downsloping is our enemy. Modeling is still an imperfect science, it is to be taken as guidance, not the say all end all to forecasting. so the recommended course of action is to wait and see. Preparations should be made to protect tender plants that have been planted out or better yet, wait until may to plant tender plants.

Thanks for reading!

-Alex