Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260304_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)
=== ===== === ==== ==== === === === ====
Wed 03/04 12Z 0.37 2918  69  17  -1 0.00
Wed 03/04 13Z 0.46 2922  65  12  -1 0.00
Wed 03/04 16Z 0.42 3020  54   8   0 0.00
Wed 03/04 17Z 0.41 2917  61   9   0 0.00
Wed 03/04 18Z 0.43 2916  65  11  -1 0.00
Wed 03/04 19Z 0.48 2816  67  14  -1 0.00
Wed 03/04 20Z 0.54 2718  64  17  -1 0.00
Wed 03/04 21Z 0.55 2718  62  19   0 0.00
Wed 03/04 22Z 0.54 2719  58  24   0 0.00
Thu 03/05 00Z 0.57 2720  59  31   0 0.00
Thu 03/05 01Z 0.55 2720  58  30   1 0.00
Thu 03/05 02Z 0.52 2719  57  28   1 0.00
Thu 03/05 03Z 0.50 2719  57  26   0 0.00
Thu 03/05 04Z 0.48 2718  56  24   0 0.00
Thu 03/05 05Z 0.45 2817  56  21   0 0.00
Thu 03/05 06Z 0.42 2816  57  20   0 0.00
Thu 03/05 07Z 0.36 2815  59  19   0 0.00
Thu 03/05 08Z 0.33 2914  63  20   0 0.00
Thu 03/05 09Z 0.28 2913  66  20   0 0.00
Thu 03/05 10Z 0.22 2910  68  21   0 0.00
Thu 03/05 11Z 0.16 2907  69  22   0 0.00
Thu 03/05 12Z 0.11 2805  71  23   0 0.00
Thu 03/05 14Z 0.07 2001  72  28   0 0.00
Thu 03/05 15Z 0.07 1602  74  29   0 0.00
Thu 03/05 16Z 0.06 1804  77  33   0 0.00
Thu 03/05 17Z 0.05 1704  77  34   0 0.00
Thu 03/05 18Z 0.05 1605  78  30   0 0.00
Thu 03/05 19Z 0.07 1607  80  27   0 0.00
Thu 03/05 20Z 0.08 1608  84  29  -1 0.00
Thu 03/05 21Z 0.10 1509  85  28   0 0.00
Thu 03/05 22Z 0.09 1510  85  30   0 0.00
Thu 03/05 23Z 0.10 1511  82  32   0 0.00
Fri 03/06 00Z 0.09 1512  82  38   0 0.00
Fri 03/06 01Z 0.11 1413  82  44   1 0.00
Fri 03/06 02Z 0.13 1415  83  51   0 0.00
Fri 03/06 03Z 0.13 1517  85  58   0 0.00
Fri 03/06 04Z 0.15 1419  86  64   0 0.01
Fri 03/06 05Z 0.17 1420  88  68   0 0.01
Fri 03/06 06Z 0.18 1421  91  72   0 0.01
Fri 03/06 07Z 0.18 1422  93  76   0 0.00
Fri 03/06 08Z 0.18 1523  94  80   0 0.00
Fri 03/06 09Z 0.18 1523  95  84   0 0.01
Fri 03/06 10Z 0.18 1522  95  89   0 0.01
Fri 03/06 11Z 0.17 1521  95  92   0 0.02
Fri 03/06 12Z 0.17 1520  95  94   0 0.03
Fri 03/06 13Z 0.17 1419  95  93   0 0.03
Fri 03/06 14Z 0.17 1419  95  90  -1 0.03
Fri 03/06 15Z 0.16 1519  94  83  -1 0.03
Fri 03/06 16Z 0.17 1519  93  74   0 0.02
Fri 03/06 17Z 0.16 1520  93  68   0 0.01
Fri 03/06 18Z 0.14 1521  93  65   0 0.01
Fri 03/06 19Z 0.14 1521  94  64   0 0.00
Fri 03/06 20Z 0.12 1620  94  68   0 0.00
Fri 03/06 21Z 0.12 1620  94  67   0 0.00
Fri 03/06 22Z 0.15 1523  93  57   0 0.00
Fri 03/06 23Z 0.12 1625  93  54   0 0.00

Run total areal avg QPF for the greens is: 0.23 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