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Pattern Fail or Fab February 2023 Pattern Thread

FallsLake said:
Yeah, the 6z 3k NAM has midafternoon temps only in the low 70s for RDU. The GFS and European are in the mid 70s. Canadian (as stated above) has mid 80s for RDU.
Click to expand...
Nam is always way to cold, it was off by 7 degrees yesterday for example, it’s a known cold bias
 
Myfrotho704_ said:
Nam is always way to cold, it was off by 7 degrees yesterday for example, it’s a known cold bias
Click to expand...
a lot of high temp forecasting is simply figuring out how deep boundary layer mixing gets during the day, since mixing will bring those air parcels at 850mb or wherever down adiabatically.

NAM 3km- puts boundary layer at 925mb Thursday afternoon for Richmond. Temp? 75.
nam3km_2023022206_fh36_sounding_KRIC.png

Different model- some WRF model- Boundary layer is around 890mb at same time. Temp? 77.
wrf-arw_2023022200_fh42_sounding_KRIC.png


Nam in my experience underestimates the height of where the boundary layer gets to, whereas the GFS is better or can overestimate sometimes. That's where this nam bias comes from.

But generally that's where a lot of discrepancies will come from, and it's all about just how the model renders turbulence and microphysics and those things are pretty hard to get right. I bet a lot of the NWS forecasts are betting that with how windy it is most models will underestimate the amount of mixing (and don't forget to add some downsloping in their for good measure)

That and cloud cover, but I think ya'll know this, if there's more clouds than forecasted Thursday (totally possible) then the highs will not be all time monthly records. lol.
 
ILMRoss said:
a lot of high temp forecasting is simply figuring out how deep boundary layer mixing gets during the day, since mixing will bring those air parcels at 850mb or wherever down adiabatically.

NAM 3km- puts boundary layer at 925mb Thursday afternoon for Richmond. Temp? 75.
nam3km_2023022206_fh36_sounding_KRIC.png

Different model- some WRF model- Boundary layer is around 890mb at same time. Temp? 77.
wrf-arw_2023022200_fh42_sounding_KRIC.png


Nam in my experience underestimates the height of where the boundary layer gets to, whereas the GFS is better or can overestimate sometimes. That's where this nam bias comes from.

But generally that's where a lot of discrepancies will come from, and it's all about just how the model renders turbulence and microphysics and those things are pretty hard to get right. I bet a lot of the NWS forecasts are betting that with how windy it is most models will underestimate the amount of mixing (and don't forget to add some downsloping in their for good measure)

That and cloud cover, but I think ya'll know this, if there's more clouds than forecasted Thursday (totally possible) then the highs will not be all time monthly records. lol.
Click to expand...
GSP doesn’t seem to be too excited about the idea of setting monthly records tomorrow. They note that the guidance that is pushing highs up over February records also start the day with clear skies… they expect that there will be cloud cover that will take most of the morning to burn off.
 
FallsLake said:
There's a small difference between the NAM and RDPS.

12z RDPS (midafternoon tomorrow):
View attachment 133488
12z NAM (midafternoon tomorrow):
View attachment 133487
Click to expand...
when it's cooler from georgia to VA like this - it's really all about differences in how the model is resolving how deep the boundary layer gets. guarantee you the rdps is a solid 100mb deeper than nam.
 
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