NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260720_0000
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 00Z 0.94 3019  71  39   9 0.00
Mon 07/20 01Z 1.17 3022  71  37   9 0.00
Mon 07/20 02Z 1.29 2924  70  44   9 0.00
Mon 07/20 03Z 1.21 3025  70  46   9 0.00
Mon 07/20 04Z 1.08 3025  70  39   9 0.00
Mon 07/20 05Z 0.86 3023  73  31   9 0.00
Mon 07/20 06Z 0.66 3122  75  25   9 0.00
Mon 07/20 07Z 0.59 3121  76  21   8 0.00
Mon 07/20 08Z 0.51 3120  76  21   8 0.00
Mon 07/20 09Z 0.49 3118  76  23   8 0.00
Mon 07/20 10Z 0.48 3117  74  28   8 0.00
Mon 07/20 11Z 0.49 3117  73  40   8 0.00
Mon 07/20 12Z 0.50 3016  72  45   8 0.00
Mon 07/20 13Z 0.53 3014  70  47   9 0.00
Mon 07/20 14Z 0.79 3014  69  43   9 0.00
Mon 07/20 15Z 2.12 2911  68  40   9 0.00
Mon 07/20 16Z 3.30 2808  68  39   9 0.00
Mon 07/20 17Z 3.59 2706  67  38  10 0.00
Mon 07/20 18Z 3.29 2506  66  38  10 0.00
Mon 07/20 19Z 2.90 2306  66  38  11 0.00
Mon 07/20 20Z 3.05 2208  69  40  11 0.00
Mon 07/20 21Z 3.18 2210  71  42  11 0.00
Mon 07/20 22Z 1.81 2211  72  43  11 0.00
Mon 07/20 23Z 0.60 2113  69  35  12 0.00
Tue 07/21 00Z 0.57 2115  68  27  12 0.00
Tue 07/21 01Z 0.59 2216  69  17  12 0.00
Tue 07/21 02Z 0.46 2115  68  13  12 0.00
Tue 07/21 03Z 0.48 2117  68  14  12 0.00
Tue 07/21 04Z 0.40 2019  66  17  12 0.00
Tue 07/21 05Z 0.53 2022  68  18  12 0.00
Tue 07/21 06Z 0.60 2025  69  17  11 0.00
Tue 07/21 07Z 0.62 2127  71  13  11 0.00
Tue 07/21 08Z 0.61 2128  73  12  11 0.00
Tue 07/21 09Z 0.56 2127  78   9  11 0.00
Tue 07/21 10Z 0.48 2126  81   9  11 0.00
Tue 07/21 11Z 0.45 2027  85   9  12 0.00
Tue 07/21 12Z 0.42 2028  87   6  12 0.00
Tue 07/21 13Z 0.39 2027  89  14  12 0.00
Tue 07/21 14Z 0.28 1927  92  38  12 0.00
Tue 07/21 15Z 0.17 1927  95  65  12 0.01
Tue 07/21 16Z 0.11 1827  96  77  13 0.03
Tue 07/21 17Z 0.05 1829  97  71  13 0.03
Tue 07/21 18Z 0.07 1730  95  59  13 0.02
Tue 07/21 19Z 0.14 1732  92  50  13 0.01
Tue 07/21 20Z 0.17 1731  91  37  14 0.00
Tue 07/21 21Z 0.15 1732  94  30  14 0.01
Tue 07/21 22Z 0.12 1732  95  56  15 0.01
Tue 07/21 23Z 0.10 1732  94  56  15 0.01
Wed 07/22 00Z 0.04 1829  94  82  16 0.01
Wed 07/22 01Z 0.08 1829  95  83  16 0.04
Wed 07/22 02Z 0.29 2027  94  76  14 0.35
Wed 07/22 03Z 0.31 2123  87  64  14 0.08
Wed 07/22 04Z 0.47 2325  79  55  15 0.00
Wed 07/22 05Z 0.46 2225  83  53  15 0.00
Wed 07/22 06Z 0.46 2224  89  56  15 0.00
Wed 07/22 07Z 0.51 2225  93  64  15 0.01
Wed 07/22 08Z 0.55 2325  95  64  15 0.02
Wed 07/22 09Z 0.59 2323  96  64  14 0.05
Wed 07/22 10Z 0.55 2322  96  62  14 0.02
Wed 07/22 11Z 0.54 2322  97  76  14 0.01

Run total areal avg QPF for the greens is: 0.72 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