Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20261013_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)
=== ===== === ==== ==== === === === ====
Tue 10/13 06Z 0.06 2802  96  96   7 0.00
Tue 10/13 07Z 0.06 2202  96  97   7 0.00
Tue 10/13 08Z 0.03 1805  97  98   7 0.01
Tue 10/13 09Z 0.08 1610  97  98   7 0.04
Tue 10/13 10Z 0.13 1618  98  99   7 0.06
Tue 10/13 11Z 0.11 1622  97  96   7 0.10
Tue 10/13 12Z 0.04 1725  97  96   8 0.10
Tue 10/13 13Z 0.04 1826  97  96   9 0.09
Tue 10/13 14Z 0.07 1829  97  87   9 0.10
Tue 10/13 15Z 0.07 1831  98  82  10 0.07
Tue 10/13 16Z 0.05 1833  97  74  10 0.07
Tue 10/13 17Z 0.06 1835  97  88  11 0.05
Tue 10/13 18Z 0.06 1836  97  93  11 0.14
Tue 10/13 19Z 0.11 1936  98  98  11 0.26
Tue 10/13 20Z 0.19 1933  98  98  11 0.16
Tue 10/13 21Z 0.25 2030  98  93  11 0.08
Tue 10/13 22Z 0.31 2128  99  86  12 0.13
Tue 10/13 23Z 0.35 2226  99  85  12 0.09
Wed 10/14 00Z 0.38 2225  99  84  13 0.08
Wed 10/14 01Z 0.43 2326  98  82  13 0.04
Wed 10/14 02Z 0.47 2325  98  76  13 0.04
Wed 10/14 03Z 0.51 2326  97  79  13 0.03
Wed 10/14 04Z 0.54 2426  97  82  14 0.04
Wed 10/14 05Z 0.55 2424  95  72  14 0.08
Wed 10/14 06Z 0.66 2427  96  78  13 0.03
Wed 10/14 07Z 0.75 2428  98  68  13 0.03
Wed 10/14 08Z 0.91 2530  98  40  12 0.04
Wed 10/14 09Z 1.10 2632  98  29  11 0.05
Wed 10/14 10Z 1.08 2731  97  18   9 0.04
Wed 10/14 11Z 0.87 2731  97  13   9 0.03
Wed 10/14 12Z 0.71 2832  95  11   9 0.02
Wed 10/14 13Z 0.65 2832  94  17   9 0.02
Wed 10/14 14Z 0.61 2831  93  14   8 0.02
Wed 10/14 15Z 0.59 2830  93  20   8 0.01
Wed 10/14 16Z 0.56 2828  92  31   8 0.01
Wed 10/14 17Z 0.58 2828  92  51   7 0.01
Wed 10/14 18Z 0.58 2927  93  58   6 0.01
Wed 10/14 19Z 0.55 2926  93  68   6 0.01
Wed 10/14 20Z 0.53 2925  94  67   5 0.01
Wed 10/14 21Z 0.50 3025  94  61   5 0.01
Wed 10/14 22Z 0.47 3024  94  57   4 0.01
Wed 10/14 23Z 0.48 3024  94  49   4 0.01
Thu 10/15 00Z 0.50 3125  94  45   3 0.01
Thu 10/15 01Z 0.52 3126  94  29   3 0.02
Thu 10/15 02Z 0.52 3127  92  27   2 0.02
Thu 10/15 03Z 0.53 3128  91  22   2 0.01
Thu 10/15 04Z 0.57 3229  90  15   1 0.01
Thu 10/15 05Z 0.52 3229  88   6   1 0.01
Thu 10/15 06Z 0.51 3230  83   4   0 0.01
Thu 10/15 07Z 0.47 3231  82   3   0 0.01
Thu 10/15 08Z 0.42 3331  81   2   0 0.01
Thu 10/15 09Z 0.36 3330  82   3   0 0.01
Thu 10/15 10Z 0.30 3329  83   2   0 0.01
Thu 10/15 11Z 0.28 3427  83   2  -1 0.01
Thu 10/15 12Z 0.22 3426  82   2  -1 0.01
Thu 10/15 13Z 0.20 3423  82   2  -1 0.01
Thu 10/15 14Z 0.15 3420  81   2  -1 0.01
Thu 10/15 15Z 0.11 3417  77   2   0 0.00
Thu 10/15 16Z 0.08 3416  69   3   0 0.00
Thu 10/15 17Z 0.08 3414  63   4   1 0.00

Run total areal avg QPF for the greens is: 2.40 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