From Walt Drag @ BOX: re: dew point problems in East

Hi and thank you in advance!

The east coast has been arid from ern nc to sne last 4 weeks including 16+ days in a row here without meas rain...yet nam and gfs dewpoint forecasts are wayyyyy tooo high during the afternoons in return flow behind the sfc high and usually too low just ahead of the cf....

I saw a soil moisture contribution graphic for the next week, and it looks far overdone.

We at kbox lower mos dewpoints during mid aftn from the top of the bl as viewed in bufkit or tsecs.

bottom line, why cant the ncep models do a better job with dewpoints which anecdotally in my mind now rank as one worst predictive elements of the model output.

This is troubling, especially since dewpoints are no longer the throwaway mos guidance we once thought... having a huge bearing on Value ADDED fire weather outlooks... as well as other applications I suspect such as air quality. I get calls from researchers on rh. Convective sounding applications.

We grid edit dewpoints but we tend not to modify the guidance often enough during the transition season...or just dont think its important enough.

any comments on additional approaches?

I presume EMC is very aware of the shortcomings of the td fcsts in mos and the models (both gfs and nam).

Just woeful the past several days (21 hr fcst 10f in error ydy from the lowest avbl 00z/30 ncep mos /fwc,met,mav/ guidance for the bulk of southern new england (sne) and ydys 45 hr fcst tds for today were in the 40s to near 50 (00z/30 fcst)!---not going to happen aznd a probable day 2 error of 8-13 degrees too wet!). we know we have a + anomaly pattern right now, yet we think the "top" of the bl is modeled very well but degrades toward the sfc on any well mixed day.

Probably most on this board agree that considerable improvement in this element would give us even better model qpf results...

in the end, we wonder if the models are mixing out the boundary layer (bl) properly to get good sfc dews and resultant bl sounding.

A byproduct of this poor element, is time devoted to dewpoint grid editing. This is an element with more importance than once thought...

HPC I suspect knows what we are taliking about with regard to the dews fcst days that they offer us in day 4-7.

Thanks for considering,

Walt Drag
Taunton-Boston (KBOX)

All --

Re: your approach to adjusting Td's using BUFKit and the top of the planetary boundary layer....that makes a lot of sense to me. That there is insufficient mixing out may also imply the BL isn't deep enough, so it may require further adjustments from even beyond that.

Re: MOS ... you say in your message that the east coast has been arid from NC to southern New England. The answer to the MOS problem is in exactly this. MOS works best when conditions are reasonably close to normal; that isn't the case at all here because MOS does a best linear fit given all observational and synoptic scale model data matchups. Dryness to this degree is well off that line *and* is poorly sampled in the data used to come up with MOS guidance, so it's not at all surprising that MOS is performing poorly. I suspect that MOS temps have been off also (too low during the day, too high at night, because of dry soils; this would be more likely true during the warm season). There really isn't much you can do about MOS in extreme circumstances except be aware of the problem and make appropriate adjustments

Re: the models themselves ... remember that soil moisture observations are not included in data assimilation systems used at NCEP. There is an attempt to keep soil moistures in line in the NAM (Eta, and soon WRF) assimilation by using actual precipitation in the data assimilation system, to avoid problems with precipitation bias affecting soil moisture. In the GFS, soil moisture is nudged toward climatology to deal with a high GFS precipitation bias. During a drought, this will make soils too moist.

Additionally, tuning of the models to work best most of the time (i.e. when conditions are close to normal) also can result in problems when extreme conditions exist. I'm not sure what contribution this would make here to the dew point problems you are seeing, though I'd suspect they'd go in the same direction as the *direct* soil moisture problems.