Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260315_0600
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 03/15 06Z 0.78 3017  90   8 -12 0.00
Sun 03/15 07Z 0.65 3018  82   9 -11 0.00
Sun 03/15 08Z 0.47 3018  76   8 -10 0.00
Sun 03/15 09Z 0.37 3017  69   8 -10 0.00
Sun 03/15 10Z 0.30 3016  59   9  -9 0.00
Sun 03/15 11Z 0.22 3113  50  11  -8 0.00
Sun 03/15 12Z 0.15 3110  39  25  -7 0.00
Sun 03/15 13Z 0.07 3206  34  55  -7 0.00
Sun 03/15 14Z 0.03 3402  34  77  -7 0.00
Sun 03/15 15Z 0.04 1503  35  92  -7 0.00
Sun 03/15 17Z 0.06 1609  39  95  -7 0.00
Sun 03/15 18Z 0.20 1512  56  96  -7 0.00
Sun 03/15 19Z 0.27 1517  73  97  -7 0.00
Sun 03/15 20Z 0.20 1622  83  98  -6 0.01
Sun 03/15 21Z 0.23 1627  80  98  -6 0.03
Sun 03/15 22Z 0.17 1632  70  98  -5 0.04
Sun 03/15 23Z 0.12 1735  67  96  -4 0.04
Mon 03/16 00Z 0.07 1739  58  87  -3 0.02
Mon 03/16 01Z 0.04 1842  54  65  -1 0.01
Mon 03/16 02Z 0.09 1844  52  81   0 0.00
Mon 03/16 03Z 0.10 1847  54  72   1 0.00
Mon 03/16 04Z 0.10 1850  61  50   2 0.00
Mon 03/16 05Z 0.07 1852  84  44   3 0.00
Mon 03/16 06Z 0.06 1852  89  34   4 0.00
Mon 03/16 07Z 0.07 1752  90  43   4 0.01
Mon 03/16 08Z 0.09 1752  90  67   4 0.01
Mon 03/16 09Z 0.08 1752  93  92   5 0.01
Mon 03/16 10Z 0.18 1650  93  97   6 0.03
Mon 03/16 11Z 0.17 1653  96  82   6 0.11
Mon 03/16 12Z 0.07 1753  97  89   7 0.16
Mon 03/16 13Z 0.05 1851  97  91   8 0.07
Mon 03/16 14Z 0.14 1851  97  73   9 0.05
Mon 03/16 15Z 0.20 1949  97  53   9 0.03
Mon 03/16 16Z 0.24 1947  96  34   9 0.02
Mon 03/16 17Z 0.25 1944  95  25  10 0.01
Mon 03/16 18Z 0.24 1941  95  27  10 0.01
Mon 03/16 19Z 0.24 1941  96  58  10 0.00
Mon 03/16 20Z 0.17 1841  95  75   9 0.01
Mon 03/16 21Z 0.06 1844  95  80   9 0.01
Mon 03/16 22Z 0.08 1849  95  88   9 0.01
Mon 03/16 23Z 0.11 1851  95  77   9 0.01
Tue 03/17 00Z 0.09 1851  95  84   9 0.01
Tue 03/17 01Z 0.07 1850  96  78   9 0.01
Tue 03/17 02Z 0.05 1849  95  85   9 0.02
Tue 03/17 03Z 0.06 1748  96  92   9 0.01
Tue 03/17 04Z 0.13 1746  96  95   9 0.02
Tue 03/17 05Z 0.16 1741  97  95   9 0.03
Tue 03/17 06Z 0.12 1831  99  98   8 0.06
Tue 03/17 07Z 0.50 2620  97  96   0 0.10
Tue 03/17 08Z 1.04 2627  95  97  -3 0.15
Tue 03/17 09Z 1.28 2427  96  91  -6 0.08
Tue 03/17 10Z 2.26 2530  97  18  -9 0.05
Tue 03/17 11Z 5.54 2533  83   8 -11 0.04
Tue 03/17 12Z 10.21 2433  79  14 -14 0.02
Tue 03/17 13Z 18.08 2433  80  25 -16 0.00
Tue 03/17 14Z 18.19 2432  74  19 -17 0.00
Tue 03/17 15Z 19.44 2431  76  21 -17 0.00
Tue 03/17 16Z 20.10 2530  73  24 -17 0.00
Tue 03/17 17Z 20.45 2530  73  28 -17 0.00

Run total areal avg QPF for the greens is: 1.31 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