NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260913_1200
Using the MB925 to MB850 layer.
Assumes Central_Greens are orthogonal to 260 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the Central_Greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Sun 09/13 12Z 0.46 2321  99  98  14 0.00
Sun 09/13 13Z 0.48 2322  98  97  14 0.05
Sun 09/13 14Z 0.46 2420  98  88  14 0.06
Sun 09/13 15Z 0.45 2319  98  78  13 0.08
Sun 09/13 16Z 0.41 2316  98  64  13 0.03
Sun 09/13 17Z 0.37 2314  97  44  14 0.01
Sun 09/13 18Z 0.39 2413  95  46  14 0.01
Sun 09/13 19Z 0.40 2512  95  54  14 0.00
Sun 09/13 20Z 0.41 2511  94  47  14 0.00
Sun 09/13 21Z 0.36 2510  92  46  14 0.00
Sun 09/13 22Z 0.38 2611  90  39  14 0.00
Sun 09/13 23Z 0.47 2614  92  38  14 0.00
Mon 09/14 00Z 0.54 2616  92  44  14 0.00
Mon 09/14 01Z 0.64 2619  91  50  14 0.01
Mon 09/14 02Z 0.82 2623  91  54  14 0.01
Mon 09/14 03Z 0.89 2626  88  68  14 0.02
Mon 09/14 04Z 0.94 2626  89  71  14 0.01
Mon 09/14 05Z 0.99 2828  96  75  12 0.06
Mon 09/14 06Z 0.91 3029  94  80  11 0.05
Mon 09/14 07Z 0.54 3023  80  78  11 0.01
Mon 09/14 08Z 0.71 2922  86  78   9 0.01
Mon 09/14 09Z 0.70 3023  89  69   9 0.01
Mon 09/14 10Z 0.63 3025  88  39   8 0.01
Mon 09/14 11Z 0.53 3127  89  13   7 0.01
Mon 09/14 12Z 0.40 3228  86   8   6 0.01
Mon 09/14 13Z 0.30 3227  81  10   6 0.00
Mon 09/14 14Z 0.24 3325  79   9   5 0.00
Mon 09/14 15Z 0.21 3323  79  12   5 0.00
Mon 09/14 16Z 0.23 3321  75  12   5 0.00
Mon 09/14 17Z 0.24 3320  72   9   4 0.00
Mon 09/14 18Z 0.34 3319  69   6   4 0.00
Mon 09/14 19Z 0.35 3319  67   5   4 0.00
Mon 09/14 20Z 0.38 3318  72   8   4 0.00
Mon 09/14 21Z 0.38 3318  77  14   4 0.00
Mon 09/14 22Z 0.36 3320  81  19   4 0.00
Mon 09/14 23Z 0.31 3322  84  17   3 0.00
Tue 09/15 00Z 0.24 3323  84  18   4 0.00
Tue 09/15 01Z 0.04 3421  77  16   6 0.00
Tue 09/15 02Z 0.06 3520  69  15   7 0.00
Tue 09/15 03Z 0.08 0018  68  14   7 0.00
Tue 09/15 04Z 0.10 0016  65  12   7 0.00
Tue 09/15 05Z 0.11 0114  59  11   8 0.00
Tue 09/15 06Z 0.10 0111  54   9   8 0.00
Tue 09/15 07Z 0.08 0206  47   6   9 0.00
Tue 09/15 08Z 0.05 0106  48   5   8 0.00
Tue 09/15 09Z 0.08 0305  48   4   8 0.00
Tue 09/15 10Z 0.04 0302  44   4   8 0.00
Tue 09/15 11Z 0.04 1102  41   3   8 0.00
Tue 09/15 12Z 0.03 1602  39   3   8 0.00
Tue 09/15 13Z 0.04 1803  39   3   8 0.00
Tue 09/15 14Z 0.05 1805  41   2   9 0.00
Tue 09/15 15Z 0.08 2005  46   2   9 0.00
Tue 09/15 16Z 0.06 1806  47   2   9 0.00
Tue 09/15 17Z 0.08 1908  47   2  10 0.00
Tue 09/15 18Z 0.12 1909  47   3  11 0.00
Tue 09/15 19Z 0.17 2010  49   4  11 0.00
Tue 09/15 20Z 0.18 2011  49   4  11 0.00
Tue 09/15 21Z 0.21 2012  46   6  11 0.00
Tue 09/15 22Z 0.23 2014  41  40  12 0.00
Tue 09/15 23Z 0.26 2116  37  77  13 0.00

Run total areal avg QPF for the Central_Greens is: 0.46 inches.

Froude Number (Frd#): 
Frd# < 0.5 Flow is subcritical and blocked.
         Upslope clouds/precip backed farther upwind of and up to mtn crest.
         W Upslope snow favors eastern Champlain Valley, BTV, and Western slopes.
         Gap winds possible.
Frd# 0.5-1 Flow is subcritical/slow moving/blocked.
         Upslope clouds/precip falls immediately upwind of mtn crest.
         W Upslope snow favors western slopes to the Green Mt. spine including:
         Montgomery,Underhill,Jericho,Bolton,Richmond,Huntington,Lincoln.
         Gap winds possible.
Frd# 1-2 Flow is critical.
         With strong winds, Mountain waves/downslope winds possible.
         Precip falls close to mountain ridge crests and on lee side.
         W Upslope snow favors Green Mt Spine,Jay,Stowe,Waterbury,NE Kingdom.
Froude > 2 Flow is supercritical/unblocked(rapid flow).
         Air flows freely over terrain.
         Persistent upslope snow not favored. Scattered snow showers and flurries.

Relative Humidity (RH): 
         925-850 mb RH > 90% needed for upslope precipitation.
         with 700mb RH > 70% favors upslope snow.
         with 700mb RH > 90% greater amounts of W upslope snow possible.

850mb Temperature (T degC) Westerly Upslope Snow Ratios: (Avg=28:1)
        T > -11       10-15:1
        T -11 to -15  25-35:1
        T < -15       15-20:1