NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260909_0000
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)
=== ===== === ==== ==== === === === ====
Wed 09/09 00Z 0.03 3405  74   0  11 0.00
Wed 09/09 01Z 0.02 3503  68   0  11 0.00
Wed 09/09 02Z 0.05 0302  66   1  11 0.00
Wed 09/09 03Z 0.04 1302  64   0  11 0.00
Wed 09/09 04Z 0.02 1704  65   1  11 0.00
Wed 09/09 05Z 0.07 1906  64   0  11 0.00
Wed 09/09 06Z 0.11 2007  71   1  11 0.00
Wed 09/09 07Z 0.13 2008  83  11  10 0.00
Wed 09/09 08Z 0.15 2010  93  70  10 0.00
Wed 09/09 09Z 0.20 2012  96  84  10 0.00
Wed 09/09 10Z 0.24 2113  96  73  11 0.01
Wed 09/09 11Z 0.27 2114  94  65  11 0.00
Wed 09/09 12Z 0.33 2216  93  61  12 0.01
Wed 09/09 13Z 0.38 2218  91  57  12 0.00
Wed 09/09 14Z 0.41 2219  92  60  12 0.01
Wed 09/09 15Z 0.41 2219  93  55  12 0.00
Wed 09/09 16Z 0.43 2219  89  44  12 0.00
Wed 09/09 17Z 0.48 2120  84  30  12 0.00
Wed 09/09 18Z 0.52 2021  83   9  12 0.00
Wed 09/09 19Z 0.60 2021  89  11  12 0.00
Wed 09/09 20Z 0.68 2024  93  76  12 0.02
Wed 09/09 21Z 0.47 2022  94  99  12 0.09
Wed 09/09 22Z 0.47 2026  97  98  13 0.15
Wed 09/09 23Z 0.58 2030  99  98  14 0.14
Thu 09/10 00Z 0.79 2235  99  96  14 0.24
Thu 09/10 01Z 0.91 2238  99  98  15 0.26
Thu 09/10 02Z 1.05 2242  98  95  15 0.22
Thu 09/10 03Z 1.22 2343  98  97  15 0.22
Thu 09/10 04Z 1.16 2342  97  97  15 0.14
Thu 09/10 05Z 1.23 2346  97  96  15 0.23
Thu 09/10 06Z 1.16 2344  97  87  15 0.17
Thu 09/10 07Z 1.10 2442  97  94  15 0.15
Thu 09/10 08Z 1.03 2539  98  93  15 0.19
Thu 09/10 09Z 0.99 2635  98  62  15 0.12
Thu 09/10 10Z 0.99 2632  97  32  14 0.07
Thu 09/10 11Z 0.99 2729  93  31  13 0.03
Thu 09/10 12Z 1.11 2729  92  18  12 0.02
Thu 09/10 13Z 1.05 2730  77  20  12 0.01
Thu 09/10 14Z 1.42 2731  79   8  11 0.00
Thu 09/10 15Z 3.10 2729  81   9  10 0.00
Thu 09/10 16Z 10.31 2728  76   7  10 0.00
Thu 09/10 17Z 12.36 2728  72   6   9 0.00
Thu 09/10 18Z 15.12 2727  79   4   9 0.00
Thu 09/10 19Z 13.05 2728  83   5   9 0.00
Thu 09/10 20Z 11.08 2829  86   7   8 0.01
Thu 09/10 21Z 2.80 2828  90   6   7 0.01
Thu 09/10 22Z 1.53 2929  92   7   6 0.01
Thu 09/10 23Z 1.10 2928  94   7   5 0.01
Fri 09/11 00Z 1.11 3028  94   9   4 0.01
Fri 09/11 01Z 0.88 3029  92   8   3 0.00
Fri 09/11 02Z 0.82 3029  92   5   3 0.00
Fri 09/11 03Z 0.76 3029  91   8   2 0.00
Fri 09/11 04Z 0.73 3031  90   5   2 0.00
Fri 09/11 05Z 0.61 3132  88   1   2 0.00
Fri 09/11 06Z 0.48 3130  87   1   2 0.00
Fri 09/11 07Z 0.44 3129  85   1   3 0.00
Fri 09/11 08Z 0.36 3128  80   1   4 0.00
Fri 09/11 09Z 0.33 3128  75   3   5 0.00
Fri 09/11 10Z 0.31 3127  72   3   5 0.00
Fri 09/11 11Z 0.32 3127  70   5   4 0.00

Run total areal avg QPF for the Central_Greens is: 2.55 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