NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260704_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)
=== ===== === ==== ==== === === === ====
Sat 07/04 12Z 0.52 3016  90  61  15 0.00
Sat 07/04 13Z 0.50 3016  90  54  15 0.00
Sat 07/04 14Z 0.60 3017  95  60  15 0.01
Sat 07/04 15Z 0.56 3016  93  68  15 0.01
Sat 07/04 16Z 0.54 3115  93  71  15 0.09
Sat 07/04 17Z 0.45 3116  93  69  14 0.12
Sat 07/04 18Z 0.44 3115  90  68  14 0.05
Sat 07/04 19Z 0.53 3014  88  73  14 0.01
Sat 07/04 20Z 0.58 3114  85  69  14 0.01
Sat 07/04 21Z 0.52 3215  83  67  14 0.02
Sat 07/04 22Z 0.48 3115  83  57  14 0.04
Sat 07/04 23Z 0.53 3215  80  49  14 0.00
Sun 07/05 00Z 0.35 3317  77  38  13 0.00
Sun 07/05 01Z 0.30 3316  73  30  13 0.00
Sun 07/05 02Z 0.34 3316  69  25  13 0.00
Sun 07/05 03Z 0.23 3415  67  25  12 0.00
Sun 07/05 04Z 0.10 3515  64  21  12 0.00
Sun 07/05 05Z 0.05 3514  62  16  12 0.00
Sun 07/05 06Z 0.05 3511  61  15  12 0.00
Sun 07/05 07Z 0.08 0009  60  15  12 0.00
Sun 07/05 08Z 0.05 0008  59  16  12 0.00
Sun 07/05 09Z 0.04 0007  59  16  12 0.00
Sun 07/05 10Z 0.04 0006  58  15  11 0.00
Sun 07/05 11Z 0.05 0007  58  17  11 0.00
Sun 07/05 12Z 0.06 0007  59  11  11 0.00
Sun 07/05 13Z 0.06 0106  61   8  11 0.00
Sun 07/05 14Z 0.15 0104  66   8  11 0.00
Sun 07/05 15Z 0.26 0102  70   7  11 0.00
Sun 07/05 16Z 0.29 0001  73   6  11 0.00
Sun 07/05 17Z 0.23 3401  76   7  11 0.00
Sun 07/05 18Z 0.22 3502  77   6  11 0.00
Sun 07/05 19Z 0.21 3502  77   6  12 0.00
Sun 07/05 20Z 0.23 0002  77   4  12 0.00
Sun 07/05 21Z 0.18 0002  77   4  12 0.00
Sun 07/05 22Z 0.20 0103  78   4  12 0.00
Sun 07/05 23Z 0.25 0304  77   4  12 0.00
Mon 07/06 00Z 0.32 0504  76   4  12 0.00
Mon 07/06 01Z 0.43 0605  75   4  11 0.00
Mon 07/06 02Z 0.68 0607  73   5  11 0.00
Mon 07/06 03Z 0.75 0709  71   5  11 0.00
Mon 07/06 04Z 0.68 0910  71   6  11 0.00
Mon 07/06 05Z 0.61 1110  72   6  11 0.00
Mon 07/06 06Z 0.49 1211  73   6  11 0.00
Mon 07/06 07Z 0.35 1412  74   6  11 0.00
Mon 07/06 08Z 0.29 1513  77   6  11 0.00
Mon 07/06 09Z 0.23 1615  78   6  11 0.00
Mon 07/06 10Z 0.12 1715  78   5  11 0.00
Mon 07/06 11Z 0.14 1714  77   6  11 0.00
Mon 07/06 12Z 0.16 1613  77   7  11 0.00
Mon 07/06 13Z 0.19 1612  77   7  11 0.00
Mon 07/06 14Z 0.21 1512  79   8  10 0.00
Mon 07/06 15Z 0.27 1512  78   8  10 0.00
Mon 07/06 16Z 0.48 1412  78   7  10 0.00
Mon 07/06 17Z 0.71 1412  77   9  10 0.00
Mon 07/06 18Z 0.84 1412  77  10  11 0.00
Mon 07/06 19Z 0.80 1513  77  11  11 0.00
Mon 07/06 20Z 0.48 1513  78  15  11 0.00
Mon 07/06 21Z 0.33 1514  80  20  11 0.00
Mon 07/06 22Z 0.26 1514  82  25  11 0.00
Mon 07/06 23Z 0.28 1515  80  33  10 0.00

Run total areal avg QPF for the greens is: 0.36 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