NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260913_1200
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)
=== ===== === ==== ==== === === === ====
Sun 09/13 12Z 0.42 2320  99  95  14 0.00
Sun 09/13 13Z 0.43 2420  98  88  14 0.04
Sun 09/13 14Z 0.41 2418  98  79  14 0.05
Sun 09/13 15Z 0.39 2417  98  68  13 0.05
Sun 09/13 16Z 0.36 2315  98  60  13 0.02
Sun 09/13 17Z 0.33 2314  96  50  14 0.01
Sun 09/13 18Z 0.36 2413  94  50  14 0.00
Sun 09/13 19Z 0.39 2412  93  55  14 0.00
Sun 09/13 20Z 0.42 2511  93  52  14 0.00
Sun 09/13 21Z 0.38 2510  91  50  14 0.00
Sun 09/13 22Z 0.42 2511  89  39  14 0.00
Sun 09/13 23Z 0.54 2515  91  40  14 0.00
Mon 09/14 00Z 0.63 2518  93  48  14 0.01
Mon 09/14 01Z 0.70 2620  92  53  14 0.05
Mon 09/14 02Z 0.80 2622  91  59  14 0.03
Mon 09/14 03Z 0.78 2622  89  73  13 0.05
Mon 09/14 04Z 0.84 2723  89  76  13 0.06
Mon 09/14 05Z 0.95 2826  96  77  12 0.06
Mon 09/14 06Z 0.98 2928  92  83  10 0.06
Mon 09/14 07Z 0.74 3022  82  80  10 0.01
Mon 09/14 08Z 0.89 2924  90  73   9 0.01
Mon 09/14 09Z 0.83 2925  91  64   8 0.02
Mon 09/14 10Z 0.84 2926  90  39   7 0.02
Mon 09/14 11Z 0.68 3028  91  17   6 0.02
Mon 09/14 12Z 0.52 3228  90  11   5 0.02
Mon 09/14 13Z 0.43 3227  86  11   5 0.01
Mon 09/14 14Z 0.38 3224  85  11   4 0.01
Mon 09/14 15Z 0.32 3322  82  13   4 0.01
Mon 09/14 16Z 0.32 3321  79  11   4 0.00
Mon 09/14 17Z 0.36 3320  77   9   4 0.00
Mon 09/14 18Z 0.49 3319  74   7   4 0.00
Mon 09/14 19Z 0.56 3219  74  10   4 0.00
Mon 09/14 20Z 0.65 3219  78  14   3 0.00
Mon 09/14 21Z 0.68 3218  81  17   3 0.00
Mon 09/14 22Z 0.62 3220  85  20   3 0.00
Mon 09/14 23Z 0.60 3321  87  19   3 0.00
Tue 09/15 00Z 0.45 3322  85  19   3 0.00
Tue 09/15 01Z 0.18 3420  79  18   5 0.00
Tue 09/15 02Z 0.07 3519  70  16   6 0.00
Tue 09/15 03Z 0.05 3517  68  14   6 0.00
Tue 09/15 04Z 0.05 3515  66  12   7 0.00
Tue 09/15 05Z 0.05 0012  60  10   7 0.00
Tue 09/15 06Z 0.07 0009  55   8   8 0.00
Tue 09/15 07Z 0.05 0106  48   6   8 0.00
Tue 09/15 08Z 0.03 0006  48   5   8 0.00
Tue 09/15 09Z 0.05 0204  48   4   8 0.00
Tue 09/15 10Z 0.03 0101  44   4   8 0.00
Tue 09/15 11Z 0.04 1301  40   3   8 0.00
Tue 09/15 12Z 0.03 1803  39   3   8 0.00
Tue 09/15 13Z 0.05 1904  39   3   8 0.00
Tue 09/15 14Z 0.05 1905  40   2   9 0.00
Tue 09/15 15Z 0.07 2006  44   2   9 0.00
Tue 09/15 16Z 0.05 1907  45   2   9 0.00
Tue 09/15 17Z 0.07 1909  46   2  10 0.00
Tue 09/15 18Z 0.08 1910  47   3  10 0.00
Tue 09/15 19Z 0.14 2011  49   4  11 0.00
Tue 09/15 20Z 0.15 2012  49   5  11 0.00
Tue 09/15 21Z 0.18 2014  45   7  11 0.00
Tue 09/15 22Z 0.21 2116  40  54  12 0.00
Tue 09/15 23Z 0.25 2118  35  84  13 0.00

Run total areal avg QPF for the greens is: 0.62 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