NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260720_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)
=== ===== === ==== ==== === === === ====
Mon 07/20 12Z 0.40 3016  78  72  10 0.00
Mon 07/20 13Z 0.41 3015  75  70  10 0.00
Mon 07/20 14Z 0.47 2914  72  69  10 0.00
Mon 07/20 15Z 0.56 2913  69  71  10 0.00
Mon 07/20 16Z 0.97 2812  67  65  11 0.00
Mon 07/20 17Z 2.12 2711  69  57  11 0.00
Mon 07/20 18Z 4.32 2510  71  55  11 0.00
Mon 07/20 19Z 5.37 2409  70  55  11 0.00
Mon 07/20 20Z 4.96 2410  70  54  11 0.00
Mon 07/20 21Z 3.76 2311  72  49  11 0.00
Mon 07/20 22Z 2.09 2312  74  45  12 0.00
Mon 07/20 23Z 0.73 2214  74  38  12 0.00
Tue 07/21 00Z 0.60 2215  72  29  12 0.00
Tue 07/21 01Z 0.63 2217  72  24  12 0.00
Tue 07/21 02Z 0.63 2218  71  19  12 0.00
Tue 07/21 03Z 0.52 2117  69  18  12 0.00
Tue 07/21 04Z 0.58 2220  71  21  12 0.00
Tue 07/21 05Z 0.58 2120  73  21  12 0.00
Tue 07/21 06Z 0.58 2122  73  21  12 0.00
Tue 07/21 07Z 0.63 2124  73  19  12 0.00
Tue 07/21 08Z 0.64 2126  75  15  12 0.00
Tue 07/21 09Z 0.56 2125  79  14  12 0.00
Tue 07/21 10Z 0.50 2125  79  13  12 0.00
Tue 07/21 11Z 0.46 2125  80  11  12 0.00
Tue 07/21 12Z 0.35 2026  83   9  12 0.01
Tue 07/21 13Z 0.37 2026  86   8  12 0.01
Tue 07/21 14Z 0.38 2027  84  11  12 0.00
Tue 07/21 15Z 0.45 1927  88  33  11 0.00
Tue 07/21 16Z 0.26 1928  89  59  12 0.00
Tue 07/21 17Z 0.12 1829  91  76  12 0.01
Tue 07/21 18Z 0.05 1831  95  63  13 0.01
Tue 07/21 19Z 0.06 1734  94  51  14 0.01
Tue 07/21 20Z 0.10 1735  96  66  14 0.02
Tue 07/21 21Z 0.07 1734  96  55  14 0.02
Tue 07/21 22Z 0.08 1733  97  73  15 0.04
Tue 07/21 23Z 0.09 1733  95  85  15 0.21
Wed 07/22 00Z 0.10 1831  95  82  15 0.20
Wed 07/22 01Z 0.11 1830  94  72  16 0.11
Wed 07/22 02Z 0.13 1929  95  69  16 0.02
Wed 07/22 03Z 0.30 2024  82  62  15 0.32
Wed 07/22 04Z 0.45 2126  85  59  15 0.04
Wed 07/22 05Z 0.55 2227  90  62  15 0.00
Wed 07/22 06Z 0.46 2224  92  58  15 0.00
Wed 07/22 07Z 0.46 2224  91  58  14 0.00
Wed 07/22 08Z 0.47 2223  91  62  14 0.00
Wed 07/22 09Z 0.48 2323  87  63  15 0.00
Wed 07/22 10Z 0.47 2321  87  60  15 0.00
Wed 07/22 11Z 0.47 2419  91  59  15 0.00
Wed 07/22 12Z 0.42 2317  95  59  14 0.00
Wed 07/22 13Z 0.40 2316  97  65  14 0.01
Wed 07/22 14Z 0.40 2215  97  68  13 0.01
Wed 07/22 15Z 0.44 2215  97  68  13 0.01
Wed 07/22 16Z 0.48 2116  95  75  14 0.00
Wed 07/22 17Z 0.61 2116  94  83  14 0.00
Wed 07/22 18Z 0.97 2117  92  72  14 0.01
Wed 07/22 19Z 1.25 2017  89  61  15 0.00
Wed 07/22 20Z 1.15 2115  90  66  15 0.09
Wed 07/22 21Z 0.54 2316  89  79  14 0.24
Wed 07/22 22Z 0.55 2517  84  56  14 0.20
Wed 07/22 23Z 0.59 2519  86  36  13 0.01

Run total areal avg QPF for the greens is: 1.61 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