NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260827_1200
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)
=== ===== === ==== ==== === === === ====
Thu 08/27 12Z 0.46 2120  88  50  13 0.00
Thu 08/27 13Z 0.51 2121  92  53  13 0.00
Thu 08/27 14Z 0.56 2121  95  67  12 0.00
Thu 08/27 15Z 0.57 2119  92  92  13 0.00
Thu 08/27 16Z 0.50 2018  93  76  13 0.01
Thu 08/27 17Z 0.42 1917  93  71  13 0.02
Thu 08/27 18Z 0.56 1919  95  65  13 0.05
Thu 08/27 19Z 0.53 1919  94  64  13 0.02
Thu 08/27 20Z 0.49 1920  94  76  14 0.00
Thu 08/27 21Z 0.54 1923  93  78  14 0.01
Thu 08/27 22Z 0.62 2026  93  70  14 0.01
Thu 08/27 23Z 0.65 2029  93  72  14 0.01
Fri 08/28 00Z 0.62 2129  87  65  14 0.00
Fri 08/28 01Z 0.63 2127  88  59  14 0.00
Fri 08/28 02Z 0.65 2227  93  70  14 0.00
Fri 08/28 03Z 0.64 2224  94  72  14 0.01
Fri 08/28 04Z 0.61 2321  95  76  13 0.01
Fri 08/28 05Z 0.58 2319  97  76  13 0.02
Fri 08/28 06Z 0.53 2317  97  78  13 0.01
Fri 08/28 07Z 0.51 2315  97  69  13 0.02
Fri 08/28 08Z 0.48 2315  97  68  13 0.02
Fri 08/28 09Z 0.47 2315  95  72  13 0.03
Fri 08/28 10Z 0.43 2414  94  64  13 0.02
Fri 08/28 11Z 0.37 2511  93  66  13 0.01
Fri 08/28 12Z 0.34 2511  93  75  13 0.01
Fri 08/28 13Z 0.32 2510  93  81  13 0.00
Fri 08/28 14Z 0.30 2509  91  88  13 0.00
Fri 08/28 15Z 0.31 2509  90  94  13 0.00
Fri 08/28 16Z 0.37 2509  91  86  12 0.00
Fri 08/28 17Z 0.51 2510  91  62  12 0.00
Fri 08/28 18Z 0.60 2610  93  35  12 0.00
Fri 08/28 19Z 0.59 2710  95  17  12 0.00
Fri 08/28 20Z 0.46 2810  96   7  12 0.01
Fri 08/28 21Z 0.34 2911  95   7  12 0.01
Fri 08/28 22Z 0.27 3011  92  14  12 0.01
Fri 08/28 23Z 0.25 3112  95  17  11 0.01
Sat 08/29 00Z 0.23 3114  94  21  11 0.01
Sat 08/29 01Z 0.21 3113  90  21  10 0.00
Sat 08/29 02Z 0.18 3112  84  22  10 0.00
Sat 08/29 03Z 0.15 3212  76  17  10 0.00
Sat 08/29 04Z 0.13 3213  66  13  10 0.00
Sat 08/29 05Z 0.13 3213  59  10  10 0.00
Sat 08/29 06Z 0.12 3213  54   8  10 0.00
Sat 08/29 07Z 0.11 3214  51   6  10 0.00
Sat 08/29 08Z 0.08 3314  51   6   9 0.00
Sat 08/29 09Z 0.06 3314  51   5   9 0.00
Sat 08/29 10Z 0.05 3313  50   5   9 0.00
Sat 08/29 11Z 0.03 3412  49   5   9 0.00
Sat 08/29 12Z 0.02 3411  47   5   9 0.00
Sat 08/29 13Z 0.03 3409  47   5   9 0.00
Sat 08/29 14Z 0.06 3206  50   6   9 0.00
Sat 08/29 15Z 0.11 3106  53   7   9 0.00
Sat 08/29 16Z 0.10 3105  55   7   9 0.00
Sat 08/29 17Z 0.20 3005  56   6   9 0.00
Sat 08/29 18Z 0.30 3006  54   6   9 0.00
Sat 08/29 19Z 0.32 3006  48   6   9 0.00
Sat 08/29 20Z 0.22 3006  45   6   9 0.00
Sat 08/29 21Z 0.21 3007  46   5   9 0.00
Sat 08/29 22Z 0.19 2906  50   4  10 0.00
Sat 08/29 23Z 0.20 2806  54   3  10 0.00

Run total areal avg QPF for the Central_Greens is: 0.34 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