NAM12 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM12 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM12_20260225_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)
=== ===== === ==== ==== === === === ====
Wed 02/25 06Z 0.22 2115  66  41 -13 0.00
Wed 02/25 09Z 0.22 2023  23  72 -10 0.00
Wed 02/25 12Z 0.22 1934  81  87 -10 0.01
Wed 02/25 15Z 0.29 2032  93  83  -8 0.07
Wed 02/25 18Z 0.32 2116  92  92  -7 0.01
Wed 02/25 21Z 0.60 2118  92  72  -7 0.01
Thu 02/26 00Z 0.63 2223  92  87  -6 0.00
Thu 02/26 03Z 0.90 2328  95  94  -5 0.05
Thu 02/26 06Z 1.48 2623  89  70  -8 0.03
Thu 02/26 09Z 2.09 2726  93  52 -11 0.01
Thu 02/26 12Z 1.31 2728  73  25 -14 0.00
Thu 02/26 15Z 1.82 2822  78   4 -15 0.00
Thu 02/26 18Z 9.54 2616  80   9 -14 0.00
Thu 02/26 21Z 7.51 2615  80  18 -14 0.00
Fri 02/27 00Z 3.15 2719  81  45 -14 0.00
Fri 02/27 03Z 0.88 2820  75  70 -15 0.00
Fri 02/27 06Z 0.61 2918  77  47 -14 0.00
Fri 02/27 09Z 0.40 2916  72  68 -12 0.00
Fri 02/27 12Z 0.34 2716  60  55  -8 0.00
Fri 02/27 15Z 0.35 2518  59  76  -6 0.00
Fri 02/27 18Z 0.45 2421  59  81  -5 0.00
Fri 02/27 21Z 0.53 2224  64  60  -4 0.00
Sat 02/28 00Z 0.61 2231  66  43  -3 0.00
Sat 02/28 03Z 0.52 2225  63  61  -4 0.00
Sat 02/28 06Z 0.62 2335  68  34  -1 0.00
Sat 02/28 09Z 0.56 2335  74  48   0 0.00
Sat 02/28 12Z 0.43 2329  76  44   0 0.00
Sat 02/28 15Z 0.38 2325  78  42   0 0.00
Sat 02/28 18Z 0.45 2423  91  51   0 0.00

Run total areal avg QPF for the greens is: 0.19 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