NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260720_1800
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)
=== ===== === ==== ==== === === === ====
Mon 07/20 18Z 3.18 2504  73  53  11 0.00
Mon 07/20 19Z 3.34 2306  73  50  11 0.00
Mon 07/20 20Z 3.58 2307  74  46  11 0.00
Mon 07/20 21Z 3.50 2208  76  42  11 0.00
Mon 07/20 22Z 2.18 2210  76  36  11 0.00
Mon 07/20 23Z 1.00 2113  73  29  11 0.00
Tue 07/21 00Z 0.71 2114  68  24  12 0.00
Tue 07/21 01Z 0.69 2116  67  21  12 0.00
Tue 07/21 02Z 0.68 2119  67  20  12 0.00
Tue 07/21 03Z 0.65 2120  68  21  12 0.00
Tue 07/21 04Z 0.70 2121  69  17  12 0.00
Tue 07/21 05Z 0.81 2223  72  17  12 0.00
Tue 07/21 06Z 0.80 2225  73  16  12 0.00
Tue 07/21 07Z 0.75 2225  73  15  12 0.00
Tue 07/21 08Z 0.75 2225  74  14  12 0.00
Tue 07/21 09Z 0.65 2123  79  14  12 0.00
Tue 07/21 10Z 0.48 2023  80  14  12 0.00
Tue 07/21 11Z 0.50 2025  84  13  12 0.00
Tue 07/21 12Z 0.48 2024  87  10  12 0.01
Tue 07/21 13Z 0.39 1923  89  21  12 0.01
Tue 07/21 14Z 0.39 1925  91  55  12 0.01
Tue 07/21 15Z 0.33 1926  93  83  12 0.01
Tue 07/21 16Z 0.25 1827  95  75  13 0.01
Tue 07/21 17Z 0.22 1828  96  84  13 0.02
Tue 07/21 18Z 0.19 1830  96  73  13 0.02
Tue 07/21 19Z 0.17 1830  97  83  13 0.04
Tue 07/21 20Z 0.10 1731  95  66  13 0.06
Tue 07/21 21Z 0.04 1632  94  64  14 0.01
Tue 07/21 22Z 0.06 1732  94  65  15 0.01
Tue 07/21 23Z 0.05 1631  97  78  14 0.02
Wed 07/22 00Z 0.05 1626  98  89  15 0.03
Wed 07/22 01Z 0.03 1724  96  87  15 0.02
Wed 07/22 02Z 0.16 1827  97  91  15 0.04
Wed 07/22 03Z 0.43 2027  93  90  15 0.02
Wed 07/22 04Z 0.54 2129  88  79  16 0.00
Wed 07/22 05Z 0.60 2227  82  78  16 0.00
Wed 07/22 06Z 0.60 2224  92  77  15 0.00
Wed 07/22 07Z 0.62 2224  96  73  15 0.07
Wed 07/22 08Z 0.65 2223  98  78  15 0.11
Wed 07/22 09Z 0.60 2221  97  63  15 0.09
Wed 07/22 10Z 0.66 2322  94  60  15 0.01
Wed 07/22 11Z 0.65 2222  97  69  14 0.02
Wed 07/22 12Z 0.69 2322  98  73  14 0.02
Wed 07/22 13Z 0.71 2320  98  78  14 0.03
Wed 07/22 14Z 0.70 2418  96  85  14 0.03
Wed 07/22 15Z 0.80 2518  94  86  13 0.02
Wed 07/22 16Z 1.10 2519  95  69  13 0.00
Wed 07/22 17Z 1.57 2421  95  51  13 0.04
Wed 07/22 18Z 1.69 2520  88  39  13 0.01
Wed 07/22 19Z 5.99 2520  78  17  12 0.00
Wed 07/22 20Z 9.44 2621  79   2  11 0.00
Wed 07/22 21Z 12.14 2622  81   5  10 0.00
Wed 07/22 22Z 7.15 2621  83  17   9 0.00
Wed 07/22 23Z 3.29 2622  86  29   8 0.00
Thu 07/23 00Z 1.52 2625  91  36   7 0.00
Thu 07/23 01Z 1.22 2725  91  39   7 0.00
Thu 07/23 02Z 0.89 2823  94  44   7 0.00
Thu 07/23 03Z 0.77 2922  95  38   6 0.01
Thu 07/23 04Z 0.55 3022  91  37   6 0.00
Thu 07/23 05Z 0.34 3223  83  37   7 0.00

Run total areal avg QPF for the Central_Greens is: 0.80 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