Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20251103_1800
Using the MB925 to MB850 layer.
Assumes greens are orthogonal to 270 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Mon 11/03 18Z 1.38 2124  77  67   2 0.00
Mon 11/03 19Z 1.39 2024  76  74   2 0.00
Mon 11/03 20Z 0.71 2026  75  86   2 0.00
Mon 11/03 21Z 0.44 1928  75  72   2 0.00
Mon 11/03 22Z 0.37 1931  78  93   2 0.00
Mon 11/03 23Z 0.76 2132  92  93   1 0.07
Tue 11/04 00Z 1.07 2331  95  93   0 0.13
Tue 11/04 01Z 1.24 2530  97  90   0 0.11
Tue 11/04 02Z 1.39 2630  98  80   0 0.07
Tue 11/04 03Z 1.40 2832  97  49   0 0.04
Tue 11/04 04Z 1.42 2932  97  36  -1 0.02
Tue 11/04 05Z 1.35 2832  96  43  -1 0.02
Tue 11/04 06Z 1.30 2831  97  56  -1 0.02
Tue 11/04 07Z 1.33 2933  97  59  -2 0.04
Tue 11/04 08Z 1.31 2935  97  60  -2 0.04
Tue 11/04 09Z 1.36 2935  97  69  -2 0.03
Tue 11/04 10Z 1.28 3036  97  82  -3 0.04
Tue 11/04 11Z 1.18 3036  97  79  -3 0.04
Tue 11/04 12Z 1.07 3135  96  80  -3 0.02
Tue 11/04 13Z 1.11 3034  96  76  -4 0.02
Tue 11/04 14Z 1.35 3032  96  32  -4 0.02
Tue 11/04 15Z 1.53 2929  96  23  -5 0.02
Tue 11/04 16Z 1.79 2928  95  31  -5 0.01
Tue 11/04 17Z 2.68 2928  92  38  -4 0.01
Tue 11/04 18Z 4.77 2829  91  44  -4 0.01
Tue 11/04 19Z 7.52 2830  88  52  -4 0.01
Tue 11/04 20Z 8.27 2931  84  52  -3 0.01
Tue 11/04 21Z 3.67 2932  82  28  -3 0.01
Tue 11/04 22Z 2.94 2933  81  18  -3 0.01
Tue 11/04 23Z 2.45 3033  81  18  -3 0.00
Wed 11/05 00Z 2.03 3033  82  30  -3 0.00
Wed 11/05 01Z 1.75 3032  83  29  -3 0.00
Wed 11/05 02Z 1.63 3031  81  23  -3 0.00
Wed 11/05 03Z 1.59 2931  81  20  -3 0.00
Wed 11/05 04Z 1.49 2930  80  15  -3 0.00
Wed 11/05 05Z 1.33 2929  80  14  -3 0.00
Wed 11/05 06Z 1.18 2928  78  13  -3 0.00
Wed 11/05 07Z 0.98 2926  73   8  -3 0.00
Wed 11/05 08Z 0.85 2924  70   4  -3 0.00
Wed 11/05 09Z 0.72 2922  67   2  -2 0.00
Wed 11/05 10Z 0.62 2920  67   3  -2 0.00
Wed 11/05 11Z 0.54 2819  65   3  -1 0.00
Wed 11/05 12Z 0.52 2719  63   6  -1 0.00
Wed 11/05 13Z 0.52 2619  57  37   0 0.00
Wed 11/05 14Z 0.54 2621  55  72   0 0.00
Wed 11/05 15Z 0.60 2520  61  87  -1 0.00
Wed 11/05 16Z 0.78 2416  69  77  -1 0.00
Wed 11/05 17Z 0.40 2216  72  92   0 0.00
Wed 11/05 18Z 0.30 2019  69  73   0 0.00
Wed 11/05 19Z 0.17 1821  58  56   0 0.00
Wed 11/05 20Z 0.14 1823  58  83   0 0.00
Wed 11/05 21Z 0.30 1825  69  98   0 0.01
Wed 11/05 22Z 0.38 1927  79  96   0 0.03
Wed 11/05 23Z 0.45 2029  88  96   0 0.06
Thu 11/06 00Z 0.51 2130  93  95   1 0.08
Thu 11/06 01Z 0.56 2230  96  95   2 0.09
Thu 11/06 02Z 0.63 2329  97  96   2 0.10
Thu 11/06 03Z 0.77 2526  98  92   1 0.13
Thu 11/06 04Z 0.89 2926  98  90   0 0.11
Thu 11/06 05Z 0.72 3341  97  93  -3 0.09

Run total areal avg QPF for the greens is: 1.52 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