Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260114_0000
Using the MB925 to MB850 layer.
Assumes Central_Greens are orthogonal to 260 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the Central_Greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Wed 01/14 00Z 0.30 2025  67  54  -1 0.00
Wed 01/14 01Z 0.37 2028  63  92   0 0.00
Wed 01/14 02Z 0.51 2032  63  95  -1 0.00
Wed 01/14 03Z 0.75 2136  76  92  -3 0.00
Wed 01/14 04Z 0.57 2134  87  91  -1 0.03
Wed 01/14 05Z 0.68 2136  71  73  -1 0.00
Wed 01/14 07Z 0.81 2233  69  77  -1 0.00
Wed 01/14 08Z 0.80 2332  73  83  -1 0.00
Wed 01/14 09Z 0.78 2331  76  69  -1 0.00
Wed 01/14 10Z 0.73 2330  78  74  -1 0.00
Wed 01/14 11Z 0.68 2328  80  65   0 0.00
Wed 01/14 12Z 0.66 2328  78  64   0 0.00
Wed 01/14 13Z 0.66 2328  78  56   0 0.00
Wed 01/14 14Z 0.65 2327  78  49   0 0.00
Wed 01/14 16Z 0.61 2324  78  42   0 0.00
Wed 01/14 17Z 0.67 2324  79  60   0 0.00
Wed 01/14 18Z 0.69 2223  79  79   0 0.00
Wed 01/14 19Z 0.74 2222  80  77  -1 0.00
Wed 01/14 20Z 0.67 2221  80  84  -1 0.00
Wed 01/14 21Z 0.62 2220  83  89  -1 0.00
Wed 01/14 22Z 0.52 2118  87  93  -1 0.00
Wed 01/14 23Z 0.42 2117  92  96  -1 0.00
Thu 01/15 00Z 0.30 2015  96  94  -1 0.00
Thu 01/15 01Z 0.28 2017  97  94  -1 0.00
Thu 01/15 02Z 0.21 1918  98  94   0 0.01
Thu 01/15 03Z 0.14 1820  96  94   0 0.01
Thu 01/15 04Z 0.11 1821  91  93   0 0.03
Thu 01/15 05Z 0.09 1721  92  92   0 0.03
Thu 01/15 06Z 0.08 1719  96  95   0 0.03
Thu 01/15 07Z 0.05 1719  98  97  -1 0.01
Thu 01/15 08Z 0.07 1718  98  94  -1 0.01
Thu 01/15 09Z 0.16 1817  98  96  -1 0.02
Thu 01/15 10Z 0.21 1916  98  94  -1 0.04
Thu 01/15 11Z 0.22 1917  98  92  -1 0.04
Thu 01/15 12Z 0.18 1916  98  92  -1 0.03
Thu 01/15 13Z 0.28 1917  98  91  -2 0.04
Thu 01/15 14Z 0.37 2016  99  81  -2 0.03
Thu 01/15 15Z 0.50 2215  99  72  -3 0.01
Thu 01/15 16Z 0.53 2315  98  65  -4 0.01
Thu 01/15 17Z 0.48 2315  97  64  -4 0.02
Thu 01/15 18Z 0.41 2416  96  60  -5 0.02
Thu 01/15 19Z 0.40 2515  95  40  -7 0.02
Thu 01/15 20Z 0.51 2516  95  23  -9 0.02
Thu 01/15 21Z 0.85 2518  94  10 -11 0.01
Thu 01/15 22Z 1.05 2519  88  11 -13 0.01
Thu 01/15 23Z 2.45 2521  83  21 -14 0.01
Fri 01/16 00Z 3.47 2521  87  29 -16 0.01
Fri 01/16 01Z 4.29 2519  90  38 -16 0.00
Fri 01/16 02Z 2.47 2519  86  45 -17 0.00
Fri 01/16 03Z 2.33 2519  83  48 -17 0.00
Fri 01/16 04Z 1.63 2619  83  46 -18 0.00
Fri 01/16 05Z 2.54 2618  84  49 -19 0.00
Fri 01/16 06Z 4.36 2718  81  69 -20 0.00
Fri 01/16 07Z 4.09 2719  84  77 -20 0.00
Fri 01/16 08Z 5.20 2819  85  81 -21 0.01
Fri 01/16 09Z 5.30 2821  85  80 -21 0.01
Fri 01/16 10Z 3.63 2822  86  76 -21 0.00
Fri 01/16 11Z 2.60 2723  86  75 -21 0.00

Run total areal avg QPF for the Central_Greens is: 0.52 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